well, it can be done even cheaper.
i don't know you find these races everywhere, but over here there often are races on grass-land (they first make some kind of track) and then you race with wrecks, no windows, no doors, no bumpers, you just place your radiator in the back, so you can bump into the oponents. there are no real limitations (only NA-engines!), there are several classes, depending on engine size. as you can figure out, the car doesn't cost shit, the rustier it is, the better.
those things are realy fun, there are several races, and then a winner comes clear (most of the time the smartest one, the one whose car's engine still works
)
a friends neighbour used to compete is these races, but with plateaus (what they're called here). that's actually just the top of the old beatle, with an home-made chassis, an engine you find somewhere, and buggy-setup. these things do cost money! (the guy quited when someone poored sand into his air filter --> tuned supra engine ready for garbage)
a vid from 2 years ago:
http://users.pandora.be/mares/nevele2002/CROSS2002.mov