I'd think that removing the carpet would expose most of the buggers. After that, I'd get a potent roach killer into every nook and cranny. Maybe close of the car and release a few bug bombs in there. (Alternately, drive it up to Chicago or Wisconsin and leave it outside with the windows down for a few days and you'll have roach ice-pops.)
You'll have to figure out if this car is worth it. For $200, you'll probably put in a lot more money to get it exterminated, cleaned and then detailed. For a 16 year old car with close to 100k miles on it, you're probably better off pitching it or selling for parts.