I got 17,980 from a dealer from kbb.com....It all depends on whether GSR's are rare where you live. Around here, they are really rare, so you could probably get that price for them, I drove 250 miles each way to get mine for 15,900. Thats a 99 GSR with 34K on it. The bluebook was 18,9xx at the time so I think that was a deal.
If GSR's are commmon where you live, then you could probably find a good deal on one. It all depends on supply and demand.
I paid $17,000 for my '99 GSR with 40,000 miles on it. They're hard to find in my area (Cincinnati). I actually called one dealer and told him I was looking for a late-nineties GSR and he said "yeah, you and everybody else".