Bill Aycock wrote:
Is this just stupid?
Probably.

My opinion: if you're going to pour time, money, and emotion into an autocross car, before choosing the car, consider what the goal is.
1. Do you want to race against your friends? What do THEY drive?
2. What kind of class are you going to run in?
3. Do you care about being competitive, and "winning," or are you just out there to have a good time?
4. Or, do you really happen to like a certain model of car, and will race one of THOSE regardless of the above?
5. Do you enjoy working on cars, or think that you might?
Those are just off the top of my head.
My sense is that for you, a DSM might fall under number 4. Especially given the comment about having wanted one back in high school (I did too). I'd also suggest that with a $500 DSM, you'd probably better respond "YES" to number 5.

There are definitely easier paths to follow, depending on your budget. You can probably find a pretty decent early Miata for a few grand.
It's totally cool to buy and run a car because you just happen to LIKE that car, warts and all. If a Talon floats your boat, and you have the time, money, and willpower to keep one going, by all means, go for it. I won't lie to you, it wouldn't be my choice, but nearly everyone in the club now thinks my taste in cars is highly suspect.