Does it have to be a real car? 
Grassroots Motorsports Spec Mini series racer:
My personal favorite:
This 1985 Toyota Sprinter was found at a junk yard with a lot of body damage due to a rollover. I purchased it for $200.00 and I intended to use it at the $2008 Challenge, but the plans fell through (2009 is a new year).
The rear hatch and hood were sourced from a blue 1984 model from the same yard for $100.00. I picked up a door panel from a white 86 Corolla for free on Craigslist to replace the passenger side panel which was FUBARd by a particularly ferocious llama one day on my driveway. The front fender was found at a local body shop and had for $100.00. I left the UPC sticker on there because I'm lazy. I did the cage on this car--it was my first one, but I think it went well. There is good clearance, and I only had to pay $450.00 for all the tubing. Oh, and I bought the wing from a guy who was replacing it with a quadruple-stack for his early-90s Civic for $50.00.
