I talked with a couple of underwater photographers on Maui and they gave me a couple of new places to take photos. We had a few days of really clear water so I ended up with some pretty decent photos.
I was surprised at both of these locations. You can drive to them both, park for free and walk right out into the water. There were several of the snorkel and scuba boats that would take you to the exact same spots but charge you $75-$90 each. A little research and talking to the right people will save you lots of money.