How much time is needed for the whale trips?

Hi,
I'm thinking of heading over to Tonga in August to swim with the Humpback Whales.
How much time is realisticly needed to do this and have a bit of a look around?
I get real bored just lying on a beach.
What would / should my budget need to be?
I'd probably want to swim with the humpback whales for four / five days or so.

Regards,

Tim

Four or five days on Vavau should be enough time to get to see the whales at least once or twice. Many won't go out on Sundays.