Hello, Sounds like you want to shoot geese everytime you go out? I don't think you will be successful everytime. I don't know anything about the goose population or areas in WI.
As for cost, some sort of clothing to break up your outline while laying in a field, a shot gun capable of shooting steel shot, decoys. what you should do is go to Cabelas and look up decoy prices they vary. 2 or 3 dozen would be a good start. if you are starting bare bones an easy 1,000 to 1,500 to start off with, that is buying cloths, waders, gun and decoys.