How is the current on the river? If you can hunt back water (no current) that is fairly shallow then you can get started pretty cheap. If there is current then you will probably need a boat or dog.

Really all you would need is a pair of waders, shotgun, shells, license, camo clothes and a few decoys. Especially on small waters I have had better luck early in the year using 4 decoys instead of 2 dozen. Try it out this way at 1st and then when you have some luck it will become a full blown obsession. You dont "need" all of that expensive equipment to shoot a few ducks but when you get into it you won't be able to help yourself from buying all of the latest gizmos!!! Give it a try! Each time out you will learn a little more and start thinking, boy it would sure be nice if I had this or that.

Good Luck!!!