I just bought a Brolin Arms, Legacy .50, in-line on e-Bay. Thought I'd try out some sabot rounds, but haven't had the chance yet.
It's made in China and has a somewhat rudimentary action, but the rear sight is very nice: adjustable for windage and elevation in small increments. It's drilled and tapped for a scope and the wood stock is a very nice dark red stain. For $80, including shipping, it's a nice beginners gun.
Grab it and have fun with it!