Hey, j-tatro, which Grand Island do you mean? If by chance you mean Grand Island, Nebraska, I can possibly help with that. As far as how much to spend, it varies. To take the initial classes, you'll need fins, a snorkel, and a mask, all of which you should get at your local dive shop, as they'll help get you fitted properly. All that will run you around $150 or so, if you get decent, but not top-of-the-line, stuff. Then there's the class fee. The open-water certification dives at the end of the class usually cost extra. Mine were $115 for the four dives. Check with your local dive shop (LDS) for rates on classes.
Welcome to the board!
-ScubaCanoe : )