If you are starting out,get a production gun and learn the basics.Go with quality either Lyman or an older Thompson Center.If you decide to give it up,they are an easy to resell.Most places carry supplies for 50cal so go with that.New guns are WAY up in price right now.TC in the $500-$600 range.Used TC run about $300-$350 and some good one were on here.If you look for used heres a couple tips.
Check the crown(end of the muzzle)and check for any nicks.When the ball leaves the barrel it will pull to that side.
Run your fingers over each of the flats on the barrel checking for any slight bumps indicating a ringed barrel from shooting without the projectile down the whole way on the charge.
Cracks in the stock from overcharging.
I am warning you that once the Blackpowder Bug bite,its very habit forming!
I would agree that a Lyman Deerstalker is an EXCELLENT gun to start with!