As in all things you get what you pay for. For an O/U that is dependable and that has withstood the test of time exspect to pay somewhere in the $1200 range. There's always a lot of good deals on used O/U's out there in the $750 -850 range.
You can always get a inexspensive O/U but ask yourself #1 is it going to hold up for the long haul and #2 if I have a problem is the service of the company any good. Browning,Beretta,Ruger,Fabarm,etc all have a proven track record. Look around and get what fits and feels good to you. Then look at the price.