I just did this as a write up for Stacy, but figured it couldn't hurt to share with everyone else.
There are five main clas s types in SCCA. Stock, Street Touring, Street Prepared, Prepared and Modified. The most realistic clas s you can run in without spending an asinine amount of money on parts and development is the Stock clas s. Stock clas s allows for the following:
-r-compound tires
-light weight wheels (but they have to be the exact same size, offset and diameter as the stock wheels.
-modified front sway bar
-modified dampers (aftermarket shocks)
-catback
-light weight battery
-air filter replacement (you have to maintain stock induction box though, so basically just a k&n drop in filter)
If it doesn't say you can modify things, chances are you cannot (this means no body kits, interior modifications too). The above list is not super expensive, you can typically build a stock clas s car for about 3.5k starting (price goes up for older cars as you have to replace a lot of things). The rest of the clas ses of autocross cost MUCH MORE. Put it this way, I've spent probably 15K developing my car and it's still not competitive in national rankings. It's going to take another 6-10K.
Now, lets look at the stock clas ses. For your budget, B-Stock, C-Stock, D-Stock, E-Stock, G-stock and H-Stock are all options for you. Super Stock is Z06's and Elises, A-Stock is Porsche's and F-Stock is new Shelby Mustangs, all three of those clas ses cost ALOT for the cars and for the tires. Below I'll go over the stock clas ses and tell you the dominant cars. I'll also post a link to what the clas s was like at the SCCA National Championship this year, that gives you a good idea at how fast these cars are compared to each other.
B-Stock (
http://sololive.scca.com/2010Nationals/BS.html)
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B-Stock is dominated by S2000's. This was the car I recommended to you on the forums. Another option is a Pontiac Solstice GXP (has to be GXP, base Solstice is another clas s), which is lightning fast.
C-Stock (
http://sololive.scca.com/2010Nationals/CS.html)
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C-Stock has one main dominant car; the 2007 MSR MX-5. RX8's are also very great regional competitors but fall short of the MSR nationally. 350/370Z's are in this clas s but may get a clas s move here in the near future.
D-Stock (
http://sololive.scca.com/2010Nationals/DS.html)
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D-Stock is a pretty wide open clas s in terms of good cars. The main front runner is the Integra Type-R. From there, you can go with a Mini Cooper S, Chevy Cobalt SS or even regular WRX's can be regionally competitive.
E-Stock (
http://sololive.scca.com/2010Nationals/ES.html)
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If someone stole the Corolla tomorrow, E-stock is where I'd go. This clas s has two VERY fun cars to drive that are pretty much the only real choices for the clas s. The 1994 Miata R or the 2nd gen (non-turbo) MR2. These are fairly cheap cars and an absolute blast to drive in E-stock trim.
G-Stock (
http://sololive.scca.com/2010Nationals/GS.html)
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G-Stock is like D-stock, in that there are lots of choices here for a competitive car. You can go with a SRT-4, final generation Celica and Mazdaspeed Protege. Locally here in DC, a Spec V does pretty good too.
H-Stock (
http://sololive.scca.com/2010Nationals/HS.html)
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H-Stock has a couple good cars, one of which you'll be lucky to find in any good condition, that car being the 89 Civic. The baseline Cooper is an excellent H-Stock car. A driver here in DC (Marshall Cone) does marvelous things with it. I've seen SVT Focus' run in H-Stock, but put the same driver in a Cooper and he/she'd be faster.
Lets summarize here. Cars worth looking into for autocross:
-S2000
-Solstice GXP
-RX8
-MSR MX5
-Integra Type R
-Mini Cooper (both S and non S)
-Colbalt SS
-Regular WRX (non-sti)
-1st gen Miata R
-2nd gen MR2 (non-turbo)
-SRT-4
-Final gen Celica
-Mazdaspeed Protege
-Spec V
Just about every other car out there is either futile in the Stock clas s rankings or will cost you an exorbitant amount of money to run in the higher clas ses. For someone who does not have a massive motorsports budget, I'd suggest staying away from any cars other than these.
THINGS TO AVOID!
-The mod bug. Dont look at cars and think, "I can make this car fast," because you cannot. Everyone out in DC has monster budgets and can outspend you within clas s restrictions. You'll wind up an "also-ran" in SM or XP, basically showing up to autocrosses just so the other people in the clas s can step on you (this is NOT fun).
-Buying parts w/out doing the research. Always ask local competitors that have national level experience for advice, especially starting off. I've been working with Corolla's for years and I still have three people right now that are national competitors that I use to pick their brains on things.
-Buying a car w/out first consulting the SCCA rule book for clas sing. You might be buying a trim level that is not allowed in a certain clas s or you might be only allowed to run certain years.
I've said it a few times in this write-up, but I cannot stress enough about the dangers of opening the spending flood gates. If you step outside of Stock clas s setup, you are either going to have to break the bank (and possibly start selling crack) just to keep up, or you're going to be just someone who gets beat by everyone each week and sits at the bottom of the time sheet. No amount of driving talent is going to trump spending out in DC, as all the other drivers on the grid are massively talented too. DC is one of the biggest SCCA hubs in the nation and has a monumental amount of great drivers.