Not a huge difference in price between the two duty free.
1L std grey goose:
NZ Duty free ~$75AUD
AU Duty free AUD $72
AU retail AUD $80

1L Grey goose VX
NZ Duty free ~AU$172
AU duty Free AUD$159
Au retail AUD $200

I've found that with decent single malt whisky retail pricing is often better than duty free pricing in either country, I guess due to the horrendous concession fees that are associated with airport duty free operations.