Well if you're looking for old ones, they won't be cheap. If you're looking for modern reproductions they're very reasonable.
The confusing part is the manufacturers...of which there are relatively few. Beretta bought Uberti which in turn owns/runs Cimarron firearms. Most of the non-extravagant models sell for around $400 a pop.
Ruger sells Vaquero models which are similar to the Uberti Cattleman line which is a copy of the classic Cold Peacemaker. Beretta makes a line of old west guns which I would imagine are just a nicer version of the Uberti line that they bought?
I bought my buddy a Uberti Cattleman for a wedding gift just over a year ago, and I picked up an 1851 Navy Conversion for myself so we could do some Cowboy shootin' together. Mine was around $500, his was perhaps $390. What are you looking to do? Shoot or collect?