The best place to start would probably be looking at TC's website
www.tcarms.comThe Encore is capable of handling most centerfire cartridges and blackpowder.
The Contender and G2 handle rimfire and centerfire cartridges. There are blackpowder barrels available for the G2. Contender barrels will go on G2 frames, and vice versa. Contender and G2 barrels will not fit on the Encore frame, which is larger.
New Encore 209x50 blackpowder rifles start around $500 for the blued/walnut version, up to about $700 for the stainless/thumbhole camo stocked version.
There has been quite a debate on this and other forums about the legalities of changing between handgun/rifle configuration (and I am in no way trying to start that debate up again!). To be on the safe side, buy your frame as a pistol frame, then add the barrels you'd like. Rifle buttstocks cannot be used with barrels under 16 inches. Similarly, some local laws specify that a handgun is designed to be held with one hand, so that may preclude use of longer rifle barrels with the pistol grip. It's up to you to make sure you comply with any local, state, or federal laws.