The Ferry cost me 3000 francs for a return ticket. The staff are quite helpful at the ferries. you can sit upstairs in the wind and sun or downstairs in the comfy chairs.
The ferry takes about 30 minutes from Papeete to Moorea and there are a few ferries running back and forth through the day.
No need to book the ferry in advance. I just rocked up and bought a ticket.
You can also take a ferry to Bora Bora , this takes 7 hours + , it is best to get the timetable so you can plan you day.
No problem with the Ferry service.