Check out Underground Racing's website. I think they list prices for their upgrades. Would you consider the Gallardo?
Edit: For Stage 1, it's $39,000 for both the Gallardo and R8. With 93 octane, you get 700 HP on both cars. With 117 octane, it's 850 WHP with the Gallardo and 1000 with the R8.
2001 M3 Coupe TiAg/Black
PSS10 Coilovers | TMS Camber Plates | LED Tail Lights | AP Headers | Two New Rear Bumpers | 219M Wheels | SuperSprint Race Exhaust | E60 Shift Lever | ZHP Steering Rack | GroupN Motor Mounts | RE Trans Mounts | AKG Subframe Bushings | AKG Diff Bushings | AKG RTABS | TMS Subframe Reinforcement |