A quick search on the net finds
VB's CASK of 9.05c in June 2008. Air NZ does not publish their CASK separtely but it can be worked out from financial statements. 30-40% is what we are told in AU and I have to assume those figures have been researched.
Out of interest the same search did bring up the cost advantage of LCC vs Legacy in US and Eurpoe.
US - Soutwest had 45% in 2001, 37% 2005
Eurpore - Ryanair 70% 2003, 60% 2007.
So it would be fairly safe to assume that JQ and PB do have a cost advantage over Air NZ when their wages are lower, fuel approx the same, and it would be safe to say overheads lower. The only cost I could think greater would be financing costs.