usually I'd say register on Gunbroker.com and search completed auctions. That will give a very good idea of realistic value most of the time. However, while there are lots of those rifles on there, only two are .454 Casull, both listed 97%+ or Exc. The higher one sold for $505, the one started at a penny with no reserve sold for $385 with 19 bids. Around $500-550 seems about right.