It all depends on the condition of the car itself, I paid $15k for mine, with only some minor modifications.
Not to mention I spent another $2k getting a few things done to it before it was back on the road. (Tyres, brakes, control arms, bushes etc)
Your best bet is to get a mechanic to check it out, to earn a few bargaining chips and try bringing the price down that way.
Having said that though, I've seen R32 GTS-4 sell for more than $20k in almost mint condition, with extremely low ks and few modifications.