2-3 g's the most, since the motor is toast and will need to be rebuilt and that can be pricey. Also, if its been sitting for a long time, its gonna need rotors, brakes, tires, suspension etc. Even though the body is in great shape, still gonna cost quite a bit to get it running right. Trust me I am going through it now. Last year I bought a 97 M3, everything working, little rough and needed wheels and was a rebuilt title for $6k. I thought I got a kick ass deal, but its been tougher than I thought and more money than I planned.
Current Rides: 964 C2
Past Rides: 94 318is, 97 M3, 01 C2 Cab, 02 330ci, 06 323i, 05 330cic M Sport, 02 M3