Little Shooter :
Some good recommendations in the previous posts.
IMHO, an O/U is NOT one of the better choices for waterfowling, especially a good one. Duck & Goose hunting is tough on the equipment .. rickety blinds, boats, dogs, clumsy shooting partners, rocks, mud, dirt, sand, water, loon s**t, snow & ice, an easy way to prematurely age a good gun. Besides wear & tear, they are difficult to load ( because they need to break open so far and often as not, when the birds are flying well, two shots is a restriction, that third shot is often neccessary. Been there, done that. I find a pump (like the 870) to have been a very dependable duck & goose gun over the last twenty years. It hasn't let me down once, not here, on the prairies & sand hills, on the Atlantic coast, up on the tundra or down in the mangroves, fresh water or salt. Its taken a lot of abuse in rock blinds and in boats, pit blinds and in all manners of nasty weather, from humid salt marshes in the high '30's to snow and ice at -20. No issues. It's like a Timex, takes a lickin' and keeps on tickin' ...
For upland hunting, I prefer a SxS, 28" barrels - 20 or 28 ga, straight stock, double triggers. For Clay targets, a single trigger O/U with 32" barrels, although I have shot lots of clay targets with 28" and 30" barreled O/U's in 12, 20, 28 & 410.
For what you have described in your original post, I would offer up a suggestion that you look at something like a Beretta 28" - 20 ga Silver Pigeon "C" as your "Upland" gun ... and get something like a standard Remington 870 Express, 28" barreled, 3" chambered gun for waterfowling. Take good care of the pretty one in the Uplands and beat hell out of the pump
in the marsh and stubble fields. Both should easily fit into your budget. The O/U will serve nicely for Skeet & Sporting with the appropriate chokes & target loads as well !
Just my 2 cents worth after owning 50-odd shotguns and 40 years in the Uplands and Wetlands ... plus a lot of recreational & competitive target shooting. And OH Yeah, FIT IS EVERYTHING !