I've bought a couple of very old Weavers, Winchester scopes and some old long tube B&L's sight unseen, but I gave so little I could have thrown them away and not have been hurt.
The prewar stuff, and even stuff postwar can be repaired- but it may not be cost effective unless it is a uncommon or desirable piece. However, applying "rare" to scope or a large dollar figure to any used riflescope no matter the vintage is ludicrous in my opinion.
Are we talking vintage or contemporary scopes here?
If it's contemporary, little or nothing is the price to pay. I've had some NIB scopes over the years and still have them, as I could never get rid of them for anywhere what I gave for them- even though they've never been mounted on a rifle and NIB. They are a dime a dozen new- even the American made ones. For instance, the new Redfield scopes are identical internally to the Leupold basic scopes, but are less expensive, and still American made. Why the difference in price? I haven't a clue...
Buyer beware, and get it cheap, or just get a new one when on sale.