You're getting good advice on this thread. Whenever a prospective new shooter asks me what guns they should buy before coming to a match my answer is always, "None. Don't buy revolvers, a rifle, or a shotgun. Come to the match and check out what people are using."
As an aside the $250 Hombres on Gunbroker are hard to to beat. The Hombres are all 4.75 inch barrels but that probably the top choice of tube length anyway. At one time it seemed like all they had was .45 Colt, then the .357s started showing up on Gunbroker and recently all I've seen on the site are the .357s. Of course a .38/.357 is a very popular chambering for cowboy.
If you have not already picked a local club, look for one here:
http://www.sassnet.com/clubs/Clubs_l...ate=California Contact the match director and let him or her know you are interested. Some clubs hold new shooter clinics or practice sessions. Otherwise they can help you navigate a regular match.