While there are overwater bungalow resorts all over the South Pacific, there are exactly 3 such resorts in Fiji itself as of now. These 3 resorts vary from one to the next, allowing guests a few choices. Of these, 2 offer rooms around the US$500 a night range while the third is suited more for those with a larger budget.
If you are looking for something other than the three listed below, you'll be able to go to one of the other islands in the South Pacific, and fortunately you'll have around 30 different resorts to choose from if you can make it to Bora Bora or elsewhere in French Polynesia. There are a few closer resorts in Samoa and New Caledonia as well, though those are less ideal than most of the others.