Hybrid-electric with regenerative braking might do well... issue with that, is that it's hard to get regenerative braking to work well enough to stop a car at the limit of tire traction, and thus not very practical for a race car.
I know of a company out in Colorado takes cars and turns them into electric vehicles
From what I hear, it's actually rather affordable (as in, less than the price of a new car), though certainly not economic- you'll never make your money back off it.
