Currency in Pitcairn Islands to New Zealand dollar (NZD NZ$). For 9.9 US dollars you can get 14 New Zealand dollars. For 99 US dollars you can get 140 New Zealand dollars. And the other way: For 9.9 New Zealand dollars you can get 7 US dollars.
And if the trip plans are simply for a given region of the world, then maybe it will come out cheaper than in Pitcairn Islands in nearby countries? See prices in: French Polynesia, Cook Islands, Niue, American Samoa, and Samoa.