Earlier this year I picked up a 19 in. '86 Trek 660 frame for $40. No wheels or saddle and a partial Shimano Ultegra 600 group on it. Some nicks and surface rust but perfectly straight and true. I converted it into a fixie for awhile and it rode fine but it was just too small for me. This looks like the identical frame.

I won't tell you how much I would pay exactly for a 21in/54cm 600 series frame, but it is a heck of a lot more than $40.