It's expensive all around I think. If you can get a room with a kitchen, groceries and farmers markets are a lot cheaper than eating out.
There is some camping options available but remember how hot and humid it is there.
You won't really need a car on most islands as they aren't to big. We hitch hiked a lot and found it pretty easy.
Jumping from island to island by plane isn't to bad. You really need to see other islands than Tahiti and Moorea.
Huahine........ about 6 years ago