The Pietta guns are nice to shoot. We have an 1860 Army and an 1858 Navy. The BP guns are a nice departure form the norm. You will definitely not burn through a bunch of ammo when shooting BP, but what you do shoot will be more satisfying than a couple of boxes full of 9mm or other modern rounds. Do a bit of reading to figure out what you need and then take it slow.
If you buy one with a steel frame, you can shoot center fire ammo by adding a cylinder
My buddy has an .50 cal BP "pirate gun" (that's what I call it as I have no experience with BP) which was a blast to shoot, but I want something with follow up shots for sure, just incase I decide to carry it as edc someday.