It's only US$0.29/min (29c) to receive calls in NZ; US$0.61/min (61c) to make calls within NZ or US$0.62/min (62c) to call back to Australia. This was the cheapest of all the SIM cards we looked at for use in NZ.
SimCardGlobal's Atlas+44 SIM card is sold by a US company, but the SIM cards are from a UK carrier and have a UK +44 phone number, as well as a US mobile number if you need to use the SIM card in the US (for New Zealand, your contacts would call the +44 mobile number assigned to you).
The upfront SIM card cost is US$73 ($74.14) which includes US$25 ($25.39) worth of calling credit. Postage to Australia is another US$17 ($17.27).
A word of warning: the SIM card will expire after 12 months, taking your credit with it, if you don't recharge within the year.