You'll want to get an island hopper airpass from Air Tahiti, the domestic carrier - not to be confused with Air Tahiti Nui, the international carrier.

A flight to/from Bora Bora only will run you about $450 per person. An airpass in 2012 will run you about $500 per person. The airpass allows you to travel within a select group of islands an unlimited amount of times within 28 days. You could also take the ferry but by the time everything is said and done the flight will cost about the same and a flight will be more convenient.

In case you haven't researched much, be aware that French Polynesia extremely expensive. You'll have to have quite a large budget set aside even if you're staying on points.