In the price range you're looking you should be able to find a used Beretta or Browning. I just picked up a Beretta 20 gauge Blackwing that appears to have not been used much, if at all. I paid $1100 for it. You should be able to find a Beretta Blackwing, Essential, Whitewing or Onyx or a Browning Citori in your price range.
There are some good deals available on Beretta BL2s, BL3s, BL4s, BL5s or their European versions, the S55, 56 or 57. They can be found at or for less than your price range. They'll be fixed choke guns but if you went with an IC/M gun you'd have 90% of your gunning covered.
I'd encourage you to shoot a 26, 28 and 30 inch O/U before you buy. You may find the 26 to be a bit short and whippy. Some guys shoot them well but others find the extra 2-4 inches of barrel helps maintain their swing and follow through. I've never found a 30 inch O/U to be cumbersome in the field. They're still shorter than a pump or auto with a 26" barrel.
Beretta is my favorite but there is nothing wrong with a Browning. I wish you enough shooting opportunities to wear one out.
