In your budget range, there are a lot of used, quality-made guns that will work very nicely. There are a few closeouts around that will also work. Browning, Beretta, SKB, Lanber are among those that can be found.
You might want to go to a gun club and see if you can borrow/rent some of them to see which ones fit you fairly close and have that "feel" that seems right to you. Try some trap or skeet to see how they work for you.
A good O/U that is reliable has more hand work than a typical pump or semi - the end result is that one with properly regulated barrels etc., will cost more than your typical pump or semi.
IF semis aren't totally out of the question, there are a few out there that will also make great field guns.
Good luck in your quest!