the "base" R8 will be aimed straight at the Porsche 911. The prices will start at around $90,000. the car will be a serious performer......and will not be as heavy as the Gallardo. It will however share many of the same components....but not so much on the base version.
the S8 and the RS8 are gonna be supercar killers. the RS8 is the rumoured 600hp (620hp is what i've been told) version, however it will likely NOT use the same engine as Lamborghini uses, because no interference between Lamborghini and Audi sales are desired. So the car will be powerful, but likely using Twin Turbo V8 powerplant rather than a big ass V10 like in the Lambo......but still, Audi has been using detuned V10s from Lamborghini in other Audis (example: Audi S8 ), so there may be a detuned turbocharged version of a Lambo V10....however Audi would rather avoid this to protect brand identity.
The RS8 will be priced well below Lamborghinis and Ferraris with similiar performance. In all likelyhood, it is designed to take on Aston Martin, SL AMGs, 911 Turbos, Maserati's next coupe, and BMWs upcoming supercar/sports car entry (shhhhhhh )