With a shotgun, you should really purchase localy, where you can shoulder the gun, see how it feels in your hands, This is a lot more important in a shotgun then a rifle. You will not hit well with a shotgun that does not fit you properly. I had a beautiful original Fox SxS that did not fit me, and try as I might, I could hit better with my rusty old Mossberg pump....
There are several good O/U out there now in the $500.00 range. Stevens, Mossberg, Charles Daly come to mind. The Russian guns are OK, but a little rough and bulky. In the $1000.00 range, the CZ's, Franchi's, used Ruger Red Lable's, Brownings Citori's, and Winchester 101's are all nice guns. Look for interchangeable chokes, and above all, good feel in your hands, and good fit. I myself am in the market for a light 28 ga for grouse over a dog. I really like the Franchi high grade O/U. Fits me great, pretty wood, nice engraving, but expensive... The standard grade gun still has nice wood, and is a lot cheaper.
Larry