Find yourself an older T/C Hawken or Renegade in .50 caliber that has a good barrel. Might cost you $350, more or less. Buy bullets, buy powder and caps. Load 90 grains of 2fg BP and a 370 grain maxi-ball, go kill stuff. It isn't that complicated.
They shoot well and are reliable. Get one that was built before the QLA feature came to be.
I read this earlier and called around. There is no one who sells black powder in my area... can the substitutes be used in the rifles you mentioned?