I have a .54 Lyman Great Plains flinter, and can recommend it highly - both the rifle and the caliber.

You can get a completed rifle from Midsouth for $489 (http://www.midsouthshooterssupply.co...u=000156031106), or a kit from T.J. General Store for $405 (http://www.tjgeneralstore.com/lyman.htm).