I picked up a Ruger Vacquero with two cylinders, a .45lc and .45 acp for $399. It has a 4 5/8" barrel, but they have a 6 1/2" model as well. Great gun, though the accuracy falls off a bit with the .45acp.
I've seen a few Smith Mountain guns in .45 acp, and I believe Taurus is making one as well. Not sure about prices though.