Never sent a frame by post to N.Z. (I live here) so don't know the cost. However there is more than one way to skin a cat.
Option One: You could purchase a frame out here and arrange delivery to a N.Z address(mind you most shops will hold it for you until you arrive. Shops here don't generally keep "frame stock". So ordering is essential.
Option Two: You buy one in the U.K. and they could post it here -Merlin/crc/on one/Wiggle seem to do this (a variety of costs-some free for a purchase over $Xxx) this may be a starting point as to who ships(they list thier couriers and how much). We have a $450 ish (not exactly sure) tax free threshold-so price needs to be below this)
Option Three: You could buy a second hand one out here from "trademe (NZ's ebay)" or vorb.co.nz classifieds.
Most stuff purchased from the U.K. which I have done has arrived within a week (despite paying cheaper rate of dispatch)
Good luck
Contact me if you have any questions ( i am going to ss worlds if you have any other questions)