I think Mike is right on. I could easily see myself pay high 50's to mid 60's for a pristine GT5S. Anything more that that, I personally wouldn't feel comfortable with.
A couple of years ago, I seen a red Amerisport GT5S with Campy clones sell for $46K. Someone got a great deal with that one. There's also a black GT5S that was discussed on this board that recently went for a similar low price. These are definitely the exceptions...or they had issues..
Europe, on the other hand, seems to "enjoy" higher prices than the US...as seen on this website:
http://www.mobile.deKevin