Thoughts on buying Coxes

Well I go up the the thrift store every so often to look for them. Other then a bunch of other crap you see and think you have to get, I've found only 1 cox engine. The engine was only a product engine out of a mid '90s plane but I did get it for like $3! I live less then a few miles away from the Minnesota state fairgrounds so I go to a lot of the events that go on there. I go to the hobby shows, antique/flea markets and the MSRA back to the 50s car show (on Sunday, they have a large swap meet near the back of it). I see a ton of Cox engines at the hobby shows but the sellers usually want too much for them. At the antique/flea markets I usually don't see too many but when i do, they are usually buried in boxes of other crap. I did pull out a sad rusted/corroded babe bee from the bottom of a metal washtub. I was only going to get it if I could get it for a dollar or less (it was just about gone, completely ruined) and the seller said "oh wow! that was a engine I had since the early 60s, lets say $15". I did try to explain to him that good nice ones sell for that and this one is well shot and all I got back was a "$10 is the best I can do". So I just walked over and put it back. I do find many other engines like a O&R 23 gas engine and some McCoys. I have also seen some original Thimble Drome champion cars and prop rods but they want like $300+ for things like that. I do find a lot of good things at the back to the 50s car show, just last time I got that Cox Jeep. So it doesn't hurt to look!