I went to Hawaii for the first time a few months ago. It was wonderful, and I'm bound and determined to live there for the first 6 months of retirement, a month or so on each island, whenever we do retire! It was THAT great! Like living abroad in an exotic place, but everyone speaks English and they drive on the American side of the road!
It IS more expensive there, that's for sure. Gas is high, electricity is high as well. The condo we stayed in didn't have a heater OR A/C - just a lot of ventilation. I asked about that, and it was explained to me that the reason was because electricity costs so much. People seem to camp a lot in places where it's allowed, at least on Kauai, though camping can't actually be permanent. (They close the parks to everyone a day or two a week, probably to make sure that no one stays permanently, and to clean up and cut grass, etc.)
Honolulu is pretty crowded, so you'll be in an urban setting there. I do hope you'll have a cost of living adjustment, as LoveTeachingMath mentioned. It's not too expensive to island-hop, so try to do it one weekend a month, if you can, especially to enjoy a varied experience.