To put a name on it, it is a standard Model 1861 contract rifle musket. I usually end up with a WAG that is too low on that CW stuff, but I would say $800-1000 tops. The gun is not in good shape, but appears to be all there. That is the kind of gun a lot of folks like to "restore", for better or worse.
Parkers' Snow made some 15,000 of them. The 1863 lockplate may have been originally made by another contractor, but there are many unknowns about those Model 1861 contracts.
Jim