Most folks are not going to go out on a limb and guess the worth of a gun like that. Too many variables. Seeing it in hand will give a better idea than looking at pictures...but even then? Location, interest and demand also matter as far as price. Guns like that are bringing much more than they were even a few years ago. But like roger said,"whatever someone is willing to pay you for it".
I can tell you that I saw a gun at two different antique gun shows a few years ago that would broadly fit into the category of what you have there. It was $400.00 at the first show and $300.00 at the next and then sold. The next time I saw it, it was $1200.00. I have no Idea if it sold, But I would not be shocked. Please don't take that to mean that the gun was actually worth any of these numbers, just that the value changes depending on who is looking at it. If you were to take a gun like that to, lets say Dixons Muzzleloading shop and try to sell it on consignment, they would give you an idea of what they might be able to sell it for based on what similar items have sold for out of their store in the past, but that is not to say that it might not be worth more of less elsewhere.....so it all depends. Having said that, I would proudly display it on the wall and enjoy it!