Foreign Minister Murray McCully is being criticised for using two different air force aircraft - with a likely bill to the taxpayer in the tens of thousands of dollars - to fly to and from Vanuatu to attend a meeting for two days.

But he is defending it as the most efficient way to attend a Pacific Island Forum meeting on Fiji, and then returning to New Zealand in time to meet Australian Prime Minister Julia Gillard.

Labour MP David Shearer says the Boeing 757 flight and the PK-3 Orion flight would have cost the taxpayer at least $75,000.

Mr McCully dismissed Mr Shearer's estimate of the cost as speculative, but could not provide the actual costs yesterday.