Well condition is everything EFH. Those muskets are pretty pricey new, something around $800/$900. I really don't know what used ones are selling for. We don't see them here very often. But I suspect a used one in "fair" shape would go for around $400 - less if there's any pitting in the bore.

I think your best bet for getting an idea of it's value would be to google the North-South Skirmish Association and see if any are listed for sale on their bulletin board.