I started with a Rem 870, no rib, modified fixed choke, 28 inch barrel. I think now an 870 Express, at $250 or under, is a good starting gun. I wouldn't buy a cheap double, as you get what you pay for and re-sale on a no-name would be difficult at best. A used Beretta 303 could be had for below your price range, and a Beretta A390 for a little more, along with the Browning Gold Hunter. Gas operated guns lessen the recoil a bit. You probably want a 28 or 30 inch barrel on a pump or auto.
Break 'em all!