You may wish to recast your query to the 'D & G General Aviation and Questions' forum but if it's of any use, check out
Euro Flight International for background info on getting a New Zealand PPL.
Rates do seem cheaper, about NZ$200/hr (£72/hr) dual for a PA28, but I wouldn't have a clue about which school is best, or indeed how current these rates are. If you believe their website, then
Aspiring Air in Wanaka (South Island) provides a good all-round experience and I'm probably heading over there myself early in Jan/Feb to get some hours in. The scenery in that part of the world is amazing, but before I get singled out by the North Island flying junta, both islands offer excellent flying challenges.
I shall watch this thread with interest.