The retail prices I'm seeing right now for new are running in the $35 to $45 range. Used on the auction sites are starting in the $15 to $20 range, closing in the $30 range. I don't think you got hurt, if the knife and sheath are in good shape.
This is one of the more popular Schrade fixed blades and has been in their manufacturing line for many years. There are enough out there that the asking price on used ones won't increase as much as some of the other models. I don't think you will be able to retire on the profit margin.
I've always liked the Schrade/Old Timer products and have carried them ever since Case XXX became so difficult to find.
Enjoy it. It is a pretty knife and is a good value.