I would recommend a diesel BMW or WV. Diesel has much better range than gasoline. both German company have a large pedigree on diesel cars winning endurance races.
Yes, the cost of safety equipment is not included in the price of the car, and while fuel cells are not required, I was thinking of including one. I was figuring that under racing conditions we'd have to stop for gas every 3 hours or so, depending on the size of the tank. maybe a little less.500 is just for the car, you can put as much as you want into making it safe. Roll cage and approved harness are a must can't compete without, big breaks needed to make hard turns. I would really suggest a fuel cell, I know that goes beyond what you want to spend but can't stay in a race if have to stop for gas every few hours.
If you were to do that we need pictures. Maybe even incorporate it into the forum's banner.Some themes are pretty funny, nothing like a bunch of guys working on a car before the race in French maids outfits.