Good luck with your search. You might also try www.searchcraigslist.org
People advertising in the ads at fiberglass
camper websites have a pretty good idea of the value of their campers and finding a great deal might be more difficult.
I paid a few hundred less than two thousand for my Compact Jr. It's a little bit of a different animal than most fiberglass campers as it has a pop up roof.
13' Scamps from the 1970's often sell for several thousand $$$$$, at prices I suspect are more than the cost of the camper when new.
But someone selling on craigslist might have had their unit for decades and aren't aware of the high demand for them.