Have my 1987 Schwinn Prologue, which I got from a guy who worked in Schwinn R&D for a long time. It's an '87 model with full Shimano Sante. The bike is in immaculate condition, save for three small marks on the chainstay. I had an offer for $750 shipped earlier in the year, but didn't feel like selling. Is $685 a fair asking price, too low? I feel like the bike is worth more than that, especially since the guy I got it form told me that there were ever only around 20 built with the Sante. He also was quite insistent that I'd never be able to find another in this shape either. Thoughts?