When you read the books written about the development of these guns, it becomes pretty clear, pretty fast, that the earlier you go, the number of surviving muskets decreases exponentially. Conclusions are drawn based on surviving guns that can be counted on the fingers of one hand, in many cases. That’s not to say there may not be more out there, hidden away as family heirlooms or whatnot, but your odds are slim, of finding a legitimate one that is assuredly original and not well into 5 figures. Especially if it has real Revolutionary War provenance.
There were thousands of besses made for the Napoleonic wars, and relatively few of the earlier ones (armies were just smaller in the 18th century, and the fighting was on a more limited scale.) Most of the guns that survived and didn’t fall prey to rust, rot, bad storage conditions (much harder to keep a warehouse full of iron and wood objects in decent condition then vs. today when we have heat, AC, weatherstripping, affordable glass windows, ventilation systems, etc.) were beaten up in training, or sold as surplus, where they were cut down and used as affordable shotguns until they were no longer shootable. Back then anything that could go bang had some value and they just got used up, unless a particular gun or six had the fortune to decorate the wall of an English country house as part of the armory of a nobleman. Only a very wealthy family could afford the luxury of storing and maintaining guns that weren’t used for some practical purpose.