A used Remington 1100 skeet or sporting would fall into your price category. Check your pawn shops. Also go to your local trap, skeet or sporting clays clubs and check their bulletin boards for some great deals in your price range. Used Benelli's are also very good and so are the Stoeger brand (same firing system). 28 inch barrel may be a little better for skeet, but 30 inch will also let you enjoy trap. Make sure you get one with interchangeable choke tubes. Ive been into the shotgun sports for a long time and these fall in your price range (new and used).
My auto is a Beretta Teknys Gold 30" but I favor my Perrazi Mirage Sporting 29 1/2" for skeet and my Browning 525 30" for trap and sporting clays. Hope this helps.
