How did you come up with $80 for a used trackball ? They are only something like $90 brand new direct from Happ, which, as well know, is more than their distributors sell for anyway.
Used mechs are only worth a few dollars. The validator may be worth something if it does work ... but I would expect that it doesn't.
In the end it's only worth what someone pays for it. Judging by the results of the auction, it wasn't worth $100.