Check the muzzleloading forums - there is lots of good advice there.
But in my opinion, you have lots of good options out there:

CVA makes several good types - they are not top of the line, but they will get the job done. I have a CVA bolt-action and have been very happy with it.

Traditions muzzleloaders are another good choice - all my hunting buddies use traditions and swear by them.

You should be able to pick up a CVA or Traditions muzzleloader with a scope for somewhere in the $175 - $250 range.

With either one, I would recommend getting a .50 cal that uses 209 ignition. Pick up a couple different kinds of bullets and see which one shoots best in your gun. A couple recommended ones are Hornady XTP & SST sabots, Barnes Expander MZ sabots, TC Shockwave sabots. If you want to go the conical route, Powerbelts are easiest to find most places and generally shoot well. Be warned with them however, use at least a 295 grain or heavier, and don't shoot them with more than 100 grains of powder.