Welcome to the Forum!
As noted,, the condition plays a BIG part of the value of any firearm. And the Old Army is a black powder gun, and sadly often are found in all stages of condition. From ANIB, to very poor due to improper cleaning.
I had a stainless OA offered to me about a year ago. There was pitting & rust inside the barrel, and the cylinder had rust as well. I offered the guy $200 for the parts gun. And I saw a fairly good looking stainless one the other day on another for sale, with a spare conversion cylinder in pretty good condition. The seller was asking $850.