the good news is that there´s no tax on motorbikes ( or cars anymore ) in NZ , but if it is a permanent import you might have to pay GST ( our VAT ) which is 12.5% . How they fix the value of a second hand vehicle I wish I knew .
NZ is a bit paranoid of importing diseases and pests , so if you don´t want to pay fumigation costs steam clean the bike before taking it in .
I don´t know if you can drive on Aussie registration in NZ , except as a temporary import , so if you have to register the bike in NZ you will be up for around 300 NZD , I would say .
And if you are planning to take a NZ bike to Aus see the information I gave someone else some months ago ( basically its harder ) .
Minimum Aussie insurance is included in the price of petrol ( AFAIK ) , and insurance is not needed in NZ . In fact , we have a cool scheme called ACC , so you never have to worry about getting sued .