I was thinking of selling my unused Leupold 50mm close focus adapter [the one placed in a butler creek flip up lip lens protector].

With a view to buying another lens on its own and having some custom built holder commisssioned, or should I canibalise it?

It cost me $40 plus shipping of say $15 = $55 Is there a market for this and if so any ideas what is a fair price?
Any guidance appreciated