I just got back from Kona and I had a great time! I dove 14 tanks with big island divers and it was totally awesome.
Kona has mantas - which was a great dive - they have this one site - called garden eel cove - first you dive it at twilight - about 80ft deep - lots of eels in the sand, nice big deep wall to go up and down.
Then once night comes the place turns into Manta Ray Heaven - there is this big pile of rocks they call the campfire and they put a big torch in the middle, all scuba divers have their lights pointed up, all snorkelers have their lights pointed down - the mantas come and barrell roll all the plankton!
I also went down to 'Red Hill' south of Kona on a long range dive. Paradise pinnacle they call it, lots of coral caves, and totally different and awesome pristine coral and critters.
A really cool dive site is just outside the harbor at Kona - I dove it twice - you get about 75 feet deep before you start back up the hill and we saw so many dolphins, an eel the size of an elephant trunk.
Anyway - I can't recommend Kona as a town enough - you'll just love it. I think it's much less expensive with more non-diving stuff to do and see as well.