yeah that might be worth the asking price. It looks like it is going to be double butted 531 with campy drop outs. (could be wrong, check the tubing sticker and the dropouts) You may be able to talk him down a little but if it comes with extras like rack and all that maybe not.
As far as converting to single speed... that may cause some debate here. I would say it would be ok... but do not remove any cable stops, braze ons, etc. The frame is about as good as it got for the era but the parts are middle of the road. Save everything you take off and then you can revert it later if you choose.