If you already have BP experience, and are wanting to dabble with half stock cap guns, try this: I go to pawn shops and small gun shops pretty frequently to see what they have. To date, I've bought many muzzleloaders in these ships for $125 or less. That includes two New Englanders and a Renegade. Bought a Traditions buckskinner, which was a fantastic little rifle, for $75 out the door. And this wasn't years ago. It's been just in the last five years or so.
The thing is this: most of the guys running these shops don't know or care about old used muzzleloaders, so they practically give them away. Back in 2014 I bought a nice Italian made .45 flintlock canoe gun in one of these shops for $100 out the door. Didn't look like it had been fired or handled much. Still have it. If you go this route just make sure they are unloaded first and give them a good cleaning. Then fire a couple blank loads, then light loads, and work your way up. And if you're broke like me, at the moment, most of these guys, at least around here, offer layaway plans. By the way, one of those little bore lights in your pocket wouldn't be a bad idea.