I pretty much always suggest folks take a look at the lower priced Browning guns althou they have climbed in price so much now I'm not sure any of the Citori line is in that price range new. BUT there are almost always some used ones around that will be. They are as good as it gets.
Other well made guns that might fall into the price range are Ruger, Beretta but likely only used, older Winchester 101s, older Charles Daly guns made my Miroku, older SKBs and Ithaca SKBs and in the new guns the CZ or DeHaan imported Huglu guns are good buys.
Avoid the Mossberg even tho it looks good it is not.
For your use I'd get 28" or 30" barrels with choke tubes. That gives you the maximum versatility in one gun to play the various clays games as well as hunt with it. These days to stay in your budget you almost have to buy used or by a Huglu.