Does it have a tubing sticker? 531 frame lots better than a Durifort. Cottered crank and Delrin RD lead me to believe that the TdF name is a little misleading. But if it's ready to ride - tires, cables, brake shoes - $100 wouldn't be out of line, but it sounds like you could get it cheaper. Plan on getting a new RD soon, though.

edit: looks a lot like the 5-F model with Sauvage "Alliage" tubing: http://www.classicrendezvous.com/Fra..._cat_pages.htm