The cheapest way, and still have decent guns would be used Ruger Blackhawks, used Marlin rifle, used SxS shotgun. Unfortunately, Remington indefinitely discontinued the 1894 & 1895 line in August and used prices are going up accordingly. A lot of folks don't think a '92 can't be competitive anymore, but it's cheap and gets you in the game. I just sold a brand new 20" Hartford 1892 .45 Colt to a new shooter for $400, and he finished 3rd overall out of 19 with it last weekend. I picked it up a year ago for $350.
I own and shoot many Uberti's, and the Cattleman works just fine, but the Rugers are a bit beefier and use coil springs. Blackhawks can be found used cheaper than Vaqueros, and adjustable sighted revolvers are legal in all age based categories as well as B Western. Fixed sight guns, on the other hand, are legal in all categories.
You should be able to find a decent 12g SxS in a pawn shop or the Nickel Paper for a couple hundred bucks. Even a single shot is legal, but you're a bit handicapped on aerial targets. A SxS
with hammers is legal in all main match categories (hammerless is legal in all but Classic Cowboy), but a '97 or '87 has certain categories it can't be used in.
Go
HERE to read the rule book - it can be a bit confusing at first.