A RTW ticket might work out okay. 140k for coach, 220k for biz. You could also get a reward ticket to say, SIN or BKK (where intl fares are often cheaper to OZ/NZ), with a stopover in NRT. I did this a few years ago, I'd double check and make sure a stopover is still allowed. I've done OZ reward travel, but not NZ. I've had some problems booking Garuda tickets this year via NW. Given the problems there, I'd probably choose another carrier.

NW has some decent fares to SIN right now, and if you use a PK36 or other discount cert, you can knock another $100 off the ticket.

I booked a PHX-DTW-MSP-PDX-NRT-SIN plus return for the mid $600's after the PK cert.