As resorts are individual private islands it is usual for the property to arrange your return domestic transfer to and from the airport in line with your arrival and departure flight times wherever possible.
If you have booked with a travel agent or operator the transfer should be part of your package.
If you have booked online you most likely will have been requested to provide your arrival flight details. Providing the resort has this information your transfer will be arranged and payment will be made direct to the resort upon your arrival.
We often receive requests for speedboat transfer rates to and from a resort. In all honesty, it is very rare that a private transfer by a local operator to and from the airport/resort will be less than the rate provided by the resort. The reason for this is that the resort will be operating group transfers throughout the day for arriving and departing guests. Whereas for a local provider not only will you need to cover the cost of the journey from the resort with you onboard, you will need to cover the cost of the return journey without you. So effectively for a return transfer, you will be charged one-way x 4 per person.
Note that if no flight information has been received by the resort your transfer Is unlikely to be arranged prior to your arrival and you should be prepared for a delay. In the event of no seats being available particularly onboard domestic flights and seaplanes during high season, you may well have to spend a night in the capital at your own expense.