well if it was just rental to drive around you can rent a new vet z06 or even a viper for 450 a day and take it to the track if you wanted to and beat the hell out of it. so if it was an all day rental with an hour of track time i would put the value at well 450-500 bucks.

but then again i wouldn't rent a car just to take out on a track, maybe a week/weekend rental if i couldn't figure out if i liked the car enough to buy it or not