First, are you prepared to pay high dollar for a good, shootable one? If so, judging by the prices at the Chantilly show, you should start thinking in the neighborhood of $10,000. The days of decent 1873's for $800 are long gone, and no one trades a 73 and boot on a new 94 any more.
Most of those guns around today at reasonable prices are in pretty sad shape. Bores are sewer pipes, the links are worn out, the carriers are loose, the wood is split, splintered or broken, and everything is a mass of rust. Dust covers are missing or are repros, parts will be repro, firing pin holes will be worn big and out of round, extractors will be broken or missing, etc.
If you are thinking of starting a collection, and have the bucks, go for it. But for a shooter, I would have to discourage you. Not only would you be taking value from the gun with every shot, a major failure would destroy a piece of history that could have been preserved.
I can understand wanting a "real" gun, but for shooting, I hope you will consider one of the very good reproductions on the market.