Good suggestions from everybody but I don't agree that a 20 gauge or even a 2 3/4 12 bore will do the work. (Sorry King)
Geese are big birds and require some killing, you can't rely on having them over the decoys at 20 yards every time.
I shoot a 3 1/2 inch 10 gauge at them and would shoot an 8 gauge if it was legal. Get a long chambered gun and you'll have something to where you won't have to pick your shots like you would with a lighter fowling piece.
A place to start might be an LC Smith Wildfowl, you see them sometimes in the $2000 range. Send it off to somebody and have the head of the stock glassed to make it stronger then fire away.
Destry
I think that Destry is on the mark. Steven Cobb and Cabelas currently have Long Range Wildfowl Elsie's. Steve Cobbs is in your price range. He has had it for awhile and may work with you on the price. It is a field grade. fxe that posts on guns international has or had a really nice long range in either ideal of specialty grade but you would need to streatch your budget significantly. It is hard to find the A.H. Fox HE long range gun. I have a 12ga Parker VH straight stock 32" bbl IM/F that is ideal for ducks or geese and Desrty shoots a similar configured DH for mostly ducks. You can pick up a damascus barreled Parker 10ga pretty easily in your price range in the GH or PH grades (there is usually a few on gunbroker). I do use a DH 10 damascus on geese in f/f chokes and it is definately a goose killer and has been for 118 years. I shoot pretty much the same payload out of the 10 and 12 gauges. The 10 gets 1 1/8oz of bismuth,ITX or Nice shot and the 12ga gets 1oz or 1 1/8oz of the same. If you reload I would recommend checking out the ITX shot and components from BPI. Good luck and enjoy whatever you choose.
