Riding in New Zealand: Routes, Advice, People and Places

can anyone help me with this?

I'm looking into costs of shipping my bike over to NZ and am happy to pay the £300 for air freight from Heathrow to Christchurch but the customs charges over there are virtually incomprehensible. I've checked the government customs site and it appears that:

• I need to pay a 48 NZD handling charge (fine)
  
• I wont need to pay any duty as it's a 0% item (fine)
  
• I might be liable to pay a 15% GST on the value o the bike (minus 33% in devaluation)
  
  

which is not fine!

on closer inspection it seems, as long as I'm returning the bike to the UK within 12 months (I am) then I can be excused from paying GST by getting a 'carnet' which is basically a guarantee for the government which I'm liable for. However it appears that the cost of a carnet is like twice the cost of the bloody GST.

Even more not okay!

References:
http://www.customs.govt.nz/features/charges/Pages/default.aspx
http://www.customs.govt.nz/inprivate/sendingitemstonz/temporaryimports/Pages/default.aspx
http://www.wecc.org.nz/services-and-resources/international-support/ata-carnets/fees,-penalties-and-claims