In my experience, autocross can be a very fun and exciting sport. I have participated in several events in my local area. I found the hobby to be very addictive as well.
Out of all my other hobbies, I think this one is the best "bang for the buck" as far as thrills go with your car. Everybody can participate. Every car (some clubs have exceptions to this though like no SUV's, no Trucks) can race. The nice thing about this kind of race is that you are competing against others in your class usually defined by the SCCA, however, you are on the course alone so there is minimal chance of hitting other cars.
The hardest part about autocross (aside from learning how to race) in my opinion is finding the right car. Sure, you can use a daily driver, but that is not recommended if you are going to participate in several events a year. Autocross can create wear on the tires and other components very quickly and can get expensive very fast. I would recommend to get a vehicle that you can use for autocross. This can be a "trailer car" or a car that you can still drive on the road, but use only for this hobby.
There are 4 key components to consider when selecting a car for autocross:
1) What type of car to get
2) The Price of the car
3) The overall condition of the vehicle (if used)
4) Aftermarket upgrades/modifications
WHAT TYPE OF CAR TO GET FOR AUTOCROSS:
For autocross racing, some people would assume that the car has to be very powerful, small, 2 doors and modified. This is not entirely accurate. While that type of car would be nice, it is not required to be competitive in autocross.
Remember that most autocross events and clubs have the cars grouped in to some sort of class. The club I participate with follow the SCCA Class guidelines. The classes help group the cars so the same "level" of vehicles can remain competitive within each class.
This is done to avoid the "biggest and fastest is best" state of thought. It would be unfair to put a heavily modified Porsche GT3 up against a stock Ford Focus. This is why they do that.
So, to pick the right car for autocross, you would probably want a coupe or convertible FIRST if possible. Sedans can work well too, but some sedans are not geared for modifications, although, the sport sedans of today are really starting to take over.
Manual transmission would be recommended, however, if you have an automatic that is OK too. You may want to consider trading it for a manual in the future to remain competitive. Again, there are still "sport shift" type automatics out there that are getting better and better each day.
Ideally, you would also want a rear-wheel drive car for autocross. RWD cars typically provide better control and handling in most cases. I know some enthusiasts out there will disagree with me, but that's OK. On the other hand, I have used several front-wheel drive cars that run with the best of them.
PRICE:
The price of buying a car for autocross is always the factor for me. I, like many others, cannot afford an expensive vehicle for autocross. There are, however, those that can afford it and price is still something for them to consider.
The $0-$5000 range:
This is the range most of us beginners want to start. Of course, free is GOOD, but consider the 3rd component (overall condition) when this option comes to mind. Several cars that can perform well and have a lot of upgradable options are the following:
1989-1997 Mazda Miata - Very nice power to weight ratio. It is VERY popular at autocross. 1979-1991 Mazda RX7 - Fast small car, handles well. Many upgrades available. 1989-1998 Nissan 240sx - Several aftermarket upgrades, handles very well. 1990-1999 BMW 3 Series - Very versatile car. You can find very nice models in this range now. 1988-2000 Honda Civic/CRX - I have seen several models compete well in autocross. 1984-1999 Toyota MR2 - Low center of gravity, great performance, mid engine. 1990-1999 Mitsubishi Eclipse/Eagle Talon - Many upgrades, some models Turbo AWD. 2000-2007 Ford Focus - Very competitive cars. SVT models available in price range. 1997-2003 VW Golf - Hatchbacks always like autocross. VR6 models available in range. 1990-1999 Acura Integra - Like the Civic, very competitive with many upgrades out there.
There may be a few more cars that I missed that fall under this price range. The method I use to hunt for cars can vary depending on the type I am looking for. I will use local classified ads, Craigslist. I will also use the bigger car searches and expand my general "hunting" area. I have successfully found great cars using VEHIX, AutoTrader as well as Government Auction Sites.
But what about the autocross cars above the $5000 range? Well, I am glad you are think that because I am about to list them below.
If you have some money to work with and want to get something newer, you can consider the following cars:
The $5,001-$20,000 range:
This range can include newer cars as well as pre-owned cars that are no more than a few years old. Remember, cars usually depreciate very fast, so as the years go by, some of the newer cars can be within reach for less money and are great for autocross. The cars below come to mind in this range:
1998-Current Mazda MX-5 - Still same basic car, but more power as they got newer. 2003-Current VW Golf - Even more modified than the previous versions, compete well. 1992-1997 Mazda RX7 - 3rd Gen is twin-turbo and can compete in autocross. 1992-2006 BMW M3 - M3's are designed for racing. Some newer models will fall in this range. 1998-2003 BMW M5 - M5's are very powerful and compete in their class well. 1994-Current Ford Mustang/Cobra - Very versatile car. Competes well in class. 1994-2002 Camaro/Firebird - Competes well in class. Many autocross upgrades. 2007-Current Mazda Mazdaspeed3 - Turbo, hatchback, competes well in autocross. 2003-2008 Nissan 350z - Great autocross car, very popular on the track. Special Autocross Kit cars such as the V6 Stalker fall in this range as well.
Now, this price range can vary in vehicles. A lot of these cars are still new and may require loans to purchase them.
The $20,001 spectrum will consist of some of the current-day models as well as the obvious "super cars" we all respect such as the Corvette, Viper, Porsche, Ferrari, Lotus and others. I will not include a list for those because if you are buying one of those for an autocross car, you did your research.
OVERALL CONDITION OF THE VEHICLE (USED):
When buying a second car for autocross, treat it like when you are buying your daily driver car. You want the car to be relatively free of major problems. Autocross racing can put stress on the car's frame, the suspension, the brakes, the tire and the overall body of the car.
You want to be sure that the car has not been in any major accidents. Frame repair or frame damage can be very dangerous mixture when you autocross. That is the MOST important thing to check for when buying a car for autocross. I have experienced and used the service by Experian called AutoCheck. They offer an unlimited number of VIN checks for one of their service options and the price is way better than the other services out there. I have used it when shopping and comes in very handy when you are checking the history of a vehicle.
The next important item to check on the car is major component problems such as smoke coming out of the back of the exhaust, major oil leaks (small leaks are expected on most used cars) slight/major overheating of the engine. Autocross is outside and you push the car to the limit. You want the major components to be in the best shape they can be. The mentioned problems can leave you stranded at the track if you do not look out for them.
I usually have some expectation to do minor repair or preventive repairs on my vehicles when I am buying to autocross them. As I stated above, small oil/fluid leaks are "OK" and can usually be fixed very easily. Small leaks tell us that the car is just used and may not be suffering from the leak as a result. Large/major leaks tell us the car may have been neglected by the previous owner and may carry residual problems unseen at the moment. When looking at a car, start it up, drive it around with the A/C engaged (even if it doesn't work). When you are finished with the test drive, leave it idling while you walk around the car continuing to inspect it. If the car has an overheating problem, often this is the time it will show. This tip has helped me avoid several beautiful autocross cars that had an overheating problem.
Belts and hoses are my most frequent "preventive" repair I do, even if they are not a problem. It is always best to know when an important component has been replaced rather than to "guess" and trust the previous owner. Water pumps, too, fall in this category sometimes.
One thing people always check when buying a used car are the tires. Yes, this is important for an autocross car, but not to see how "good" the tires are, but to see if the car needs an alignment. Autocross is about handling and you need to be sure the car's stock "handling" ability is where it should be.
Why not worry about the tires? Well, tires should be one thing to consider buying for your autocross car to begin with, so the existing tires should be removed anyway. Tires are probably the most bought wear item an autocross member will buy. A lot of autocross racers will bring a set of tires for racing, one for driving home (those who do not use a trailer) and some will even bring spares for the racing tires. This is so common that Tire Rack offers tires just for autocross. I have used them and they are the best place to get tires for this.
AFTERMARKET MODIFICATIONS FOR AUTOCROSS:
If you ever look into the aftermarket world of the auto industry, you know that there are literally thousands of places to look and buy. I will list a few spots that most people do not think to look, but surprisingly have things for the autocross fans.
First and foremost, autocross cars do NOT always need major upgrades to be competitive. A driver can use a stock vehicle and compete against fellow stock vehicles and remain competitive. Once you start to modify or upgrade heavily, you may start to move into different classes and compete with other cars that are equally modified. Keep that in mind when you want to change something.
Usually, I say modify the easy things first: Intake, exhaust and general tune ups. Most autocross drivers do not go far from that. These should be the first things you try to upgrade while you participate in autocross to get the most performance out of your vehicle.
If you decide to go further to be more competitive, my next recommendation would be suspension and body roll modifications. Please remember, certain upgrades in this area may change your class. Be sure to check your club or groups rules with these modifications.
Usually, the fastest upgrade to an autocross car would be front and rear strut tower bars/braces. They are usually inexpensive to buy and easy to install. They are also very modular meaning that when you buy these, they will work with other suspension components in place (usually). This modification helps stiffen the car's suspension and frame and helps with cornering.
The next modification recommendation would then be the front and rear sway bars and links. These parts also help the body roll while cornering and handling and can sometimes be modular to the suspension system as a whole.
The final suspension upgrade is usually the most expensive: The struts (shocks/springs). This upgrade usually works well with the above items, but ads more stiffness, more response to the handling and sometimes lower the car overall for a lower center of gravity.
Once you have modified the entire suspension, my next recommendation would be to upgrade the brakes (at least the pads). This will help your stopping ability for those moments where a tap of the brake is needed during a lap. Please keep in mind that high performance brake pads usually wear much quicker than OEM.
One of the last things I recommend to upgrade is the tires. Now, I'm not saying that you should not FIRST buy new tires when you autocross, but I am saying not to UPGRADE them to an autocross/race tire just yet. Most autocross enthusiasts will tell you to get used to the stock/regular tires on your car first.
Once you get used to stock type tires, modifying them to a race tire or softer tire will actually improve your lap times (that's the theory anyway).
One last note. I recommend replacing the fluids in your car with as many synthetics as you can. Synthetic fluids have higher heat resistance and can take the intense moments you will be putting on the car during the autocross laps.