The V8 Supercars are about 1300kg, not much less than current mustangs, have 650hp (fwhp I believe), are basically a tubular chassis/cage with car skin around it, racing
suspension, better aerodynamics, and 10 inch slicks, and they have to be relatively gentle with the car when it is dry, on a race track!
Now, you would like the same (more I think, you did say rwhp right?) power with
suspension, chassis, tyres, that offer much less than the V8 Supercar setups.
(The above was just to give you some perspective on what 650hp is)
Myself, if I were building the car for 650hp, I would put a cage in, racing seats and harnesses, the best
suspension I could find, the best clutch, driveshaft, diff, brakes, and tires I could find. I guess this would cost a *little* more than 6k (with the cost of the 650hp motor included).
This would be insane for a street car, big pain to get in and out of, and to drive, etc. Like most others said, 400 would be plenty, especially to start with.