Sarge-

The accuracy of any answer is going to have to take into consideration *when* you plan to purchase, what the value of the dollar will look like then, also action type and condition.

I'm going to guess, from my 'not at all a victorian firearms appraiser' standpoint, that current value on a J&W Tolley Jones underlever back action hammer double rifle in shooting condition (tight on face, no mechanical problems, regulates with a known load), without the case, tools, mould etc. is going to run in the $25,000 - $35,000 range with today's US dollars.
That's my guess.

I'm interested to see what the guys who are much more 'in the know' will have to say.

--Tinker