First off, forget the pawnshops. Believe me, you're going to get gouged. And probably on a rifle with a pitted bore, too. Instead, set your sights to Midsouth Shooters Supply. You can get a Lyman Great Plains Rifle for $295 and you get the choice of .50 or .54 caliber. The Great Plains is a wonderful rifle and will provide you with loads of fun. It's a pretty close copy of an actual Hawken rifle (lots of ones called "Hawkens" by CVA and T/C don't look anything like a real Hawken; the Great Plains looks like an actual Hawken and is made fairly similar, too.) The Great Plains in .54 is a lot of fun and boy does it blow stuff to pieces! And pretty darn accurate, too. Just foolin' about, my .54 GPR put 30 balls through a hole the size of a quarter at 25 yards. The GPR comes with a 1-60" rifled barrel made for patched round ball whch is also the cheapest way to go for shooting. But if you want to ry your hand at conicals, you can buy a 1-32" rifled barrel for shoting conicals. It costs $125 from Midsouth. See, the GPR has a hooked breech, so the barrel lifts right out after you punch out the two removable retaining keys. Makes it easy to clean. And easy to change barrels. I highly suggest the GPR.
Now, for a little more money, you can get you a .58 Enfield or Springfield from any Civil War sutler or from Cabela's. These cost around $400 to $500. The conicl mines are pricey, but you can fire round balls, too, though the .58 round ball costs you a tad more than .54 or .50 round balls. Depends on what "era" you like best---Civil War, Mexican War (you might like the 1841 Mississippi Rifle), Fur Trade Era, Gold Rush, Bleeding Kansas (you can get a paper-cartridge firing 1859 Sharps), etc.
Now, I see you're not a hunting man. I bought a .54 to be able to down large game as well as for the fun of shooting .54 cal. But you might be better served by a .50 cal GPR if you want to go that route. You can get rifles in .45 and the balls are a tad cheaper than .50s, but most of the .45s don't have removeable barrels and are a tad more difficult to clean. If you're looking for a "modern" inline muzzleloader, the best one I've seen is the Ruger "Officer's Model". Just about all inlines are going to be .50s and above and made to fire conicals, though I hear tell they shoot round ball tolerably well. I wouldn't know because I've never fired an inline.
But the best all-around value I think you're going to find is the Great Plains rifle from Midsouth. It also has a double set trigger set up that is adjustable.
I suggest steering clear of CVA and especially a used CVA.