Check out some of the auctions houses online for what they're going for...Rock Island, James D. Julia, Amoskeag, Butterfields, Christies, Drake, J.C. Devine, Sotheby's, Kull & Supica etc.
I've seen them in the high six figures and for a few hundred dollars--depending mostly on bore relative to model...Some models or grades there were only a few made in a specific chambering and they can be worth lots, even in worn condition...