The
Spira is a really neat car. It weighs 302lbs, seats two in tandem, and is made of foam, fiberglass, and aluminium. The drag coefficient looks a little high among x-prize cars, but it's got a small frontal area. Still, imagine what it could do with a boat-tail.
I think this is what BicycleBob was talking about when he said that a car should weigh no more than its passengers, and that if you design it like a bicycle helmet that envelops the driver, it should be reasonably safe.