It doesn't necessarily have to become a terribly expensive hobby. Certainly not as bad as buying a boat or doing a car restoration.
The first thing to resolve is whether the barrels are sound and safe to shoot. This includes an evaluation of internal and external pitting, dents, loose ribs, etc., along with barrel wall thickness measurements. That is the one determining factor as to whether this gun should be repaired and fired, or simply cleaned up and hung on the wall.
Someone here should be able to steer you towards an Oregon area muzzleloader gunsmith who can pull the locks without doing damage, and tell you at a reasonable cost what the problem is, and how much it should cost to repair it. Handing someone you don't know a gun and a blank check can get you in trouble. Once the gun is functional, the cost of black powder, wads, shot, and percussion caps isn't much more than modern ammunition, and certainly less than most of the non-lead stuff.
