No visa is required of passengers and crew who visit while their vessel is at Pitcairn.
Anyone wishing to stay on Pitcairn after the ship has left requires a residence permit issued by the Commissioner for Pitcairn Islands, Pitcairn Island Administration, Auckland, New Zealand. Applications must be approved by the Island Council and the governor, and a processing fee is payable in advance.
If granted, a "license to land and reside" on Pitcairn for up to six months costs extra. You'll be asked to provide a specific reason for wanting to go (journalists are not welcome).
New Zealand currency is used, with local Pitcairn coins. No bank exists on Pitcairn, but the island secretary will change foreign cash and traveler's checks.