The good news is that the gun isn't priceless...which means the gun can be sympathetically cleaned up (and gently, lest you lose patina) and shot.
I can't think of anything more fun than taking a few upland birds with that old gun. Have the gun checked out for safety's sake and enjoy shooting her occasionally when she's not hanging on the wall.
As for appraised value, too many things are still unknown including the condition of the bores and other factors, but I'd imagine its in the $1000 range, +/- $800. Probably more on the low side. Again, a perfect reason to deactivate the rust, clean the bores, and go have a great time shooting that piece of 150 year old functional art.
