Megolith -
I guess my chief concern would be your qualifications to run someone else's car. Bail procedure, chute, fire suit, qualifying for different licenses - no two cars are the same, and there are a lot of questions to answer.
If you're looking to buy a cheap thrill, I'd find an early 90's 5 liter Mustang, rip the mufflers off and run the 130 club. Less liability on everyone's part.