IMO flightsdirect.co.nz seems to be a good search for flights. Would cost a couple of thousand more to travel in the next couple of months compared to next Feb.
It annoys the hell out of me also that the same Air NZ flight originating in the UK is 30% cheaper than if it originates from NZ - WHY???? It's the same flights - same aircraft - same fuel - same staff! They are just gouging us for more money again - phew - deep breath - step off soapbox.
Just searching on STA whilst venting and they do seem to have some good flights.
Good luck - please let us know who you end up booking with.