This will be one of your biggest expenses alongside the accommodations, so let's start with how you're actually going to get to French Polynesia.
Paying cash for your flight isn't going to be the cheapest but there are ways to keep the prices down. There's no guarantees for getting the “best deal” but there are a few steps you can follow.
This doesn't work so well if you have specific dates in mind, but if you're just waiting for killer fare to jump on, you just need to be constantly on the lookout.
If you have specific dates in mind, you can set up one or many price alerts to start tracking what the trend is on flights.
You don't have to be locked into the round trip from your home airport to PPT, especially since some low-cost carriers don't appear on aggregators like Skyscanner or Kayak.