First off.... regarding you other post on caliber.... If you will shoot RB's .54 hands down. I have never shot conical for anything except to try them years ago and gave up after about 20 or so shots. A.54, with a RB,as others have said, will take about everything on the NA continent.
Now, on to the gun.... You want a flint Hawken gun.... The best way to get that is build it yourself or buy one already built that fits within your budget. The already built guns will not be cheap but if done by a good builder worth the money. I just saw a really nice flint full stock on a table at a show in KY for $1500.00 (great wood and parts, perhaps just a bit high on price) and it was a .58 cal.