I would suggest going to a large Civil War reenactment or N-SSA skirmish. Used guns can be found among the sutlers there. This has the advantage of letting you inspect the gun in person, and also to bargain for a better price. You can also compare the offerings of different sellers, all in one place.
Cap and ball revolvers, new and used, are bargains in the gun world. This is due, I think, to them never having been threatened by adverse gun legislation, and therefore, never having been subject to panic buying. Right now, there is also a favorable exchange rate with the euro.