Best bargain out there is a used Browning Superposed....many can had for $1000 or less. These are extremely high quality, Belgium made, and will only go up in value. Down side is the fact they all are fixed choke barrels....pre-choke tube era. 12 gauge is the most popular for upland bird hunting and trap.
If you're finding Belgian Superposeds for under 1 grand, please share....the best I am seeing is closer to 2....
Another brand worthy of consideration is SKB - for both O/U and SxS; however, a decent SxS, especially one able to withstand the rigors of trap and hunting, will cost more than 1,000 used - most in that range will be field guns- light and agile, but brutal for trap or long shooting sessions.
For trap and pheasants, a 12 will be your best bet, although a well-made 20 will also work.
Closer to your price range in SxS will be a used Savage/Stevens, either the 311 or the Savage/Fox B series.
For a touch over 1,000 there is the used Ugartechea, a well-made Spanish SxS.
With 1,000 as your budget, IMO, I would be looking for a well-made used O/U field grade gun from SKB, Browning or Beretta. Realize, as mentioned above, field guns are lighter and will have more recoil compared to a similar model target gun. Which activity do you envision doing more of? If you're hunting every day, putting in mile after mile, and only shooting a few rounds of clays to get ready for hunting, go with the field model. If the opposite is true, where you'll be shooting thousands of clays per year and doing some bird hunting, then get the heavier target model and live the weight in the field.