You can save a lot of money by shore diving on your own without a guide. Unfortunately, unless you're familiar with Hawaii's marine life, your experience won't be as good as if you had a guide. On Maui, it's as simple as going to Maui Dive Shop and getting one of their free magazines that has information about the shore diving sites, including graphics. Then you rent a tank, weights, and a flag (about $15) from any of the dive shops on the island, and head out to one of the sites.
Remember that Hawaii has a lot of endemic species that you cannot see anywhere else in the world. Without a knowledgeable guide, an inexperienced Hawaii diver is going to miss a LOT. Actually, I'd venture to say you'll miss most of what there is to see. Of course an experience Hawaii diver or local may be just as good as a professional for guiding, so you can always post the dates you're on island (in a separate thread when you get closer) and see if anyone is available to dive with you.
I believe Shaka Doug is $89 for a 2-tank guided shore dive, which is a good $40 (or more) cheaper than a boat dive. The nice thing about Doug is that he has his scuba bus with everything a diver needs for a fun dive. That means you simply meet him at the dive site and he has everything ready for you instead of you having to pick up tanks, etc.