Currency in Pitcairn Islands to New Zealand dollar (NZD NZ$). For 10 US dollars you can get 16.6 New Zealand dollars. For 100 US dollars you can get 166 New Zealand dollars. And the other way: For 10 New Zealand dollars you can get 6.27 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.