Is this a club associated with a high school, or is it a private club? There are different considerations for each type of organization, the most important of which is liability. Assuming you can get over those hurdles, fundraising ideas include bake sales, auctions of donated goods and services, car washes, Christmas tree sales, spaghetti feeds, chocolate bar sales, coupon book sales, etc. Just do a Google search on "student fundraisers" and you should find all sorts of sources and ideas.
For high school students seeking to learn how to scuba dive, I might suggest finding a local Venture Crew (a branch of Boy Scouts of America) that focuses on diving. Both boys and girls of high school age can join a Venturer Crew. A club-like structure already exists, they already have established relationships with local shops and instructors, they have financial support and fundraising events, trips, a nice fat insurance policy, and pretty much anything else you might need. The fact that the Venturing program allows a Crew to dedicate itself to a single emphasis makes it a very different program from a typical Scout Troop.
