Hi Grinch,
One snippet of information you would need to consider is that driving diesel cars in NZ attracts a levy for the extra polution they create. On the flipside, diesel is also a much cheaper fuel!

At risk of contradicting myself, there are plans in NZ to upgrade their diesel fuel as it is still a heavy polutant (something like 500 micrograms of something per whatever instead of the 50 micrograms found elsewhere in the world! Sorry i'm missing the science bit, just cant remember!) so things may have changed again by the time you get there!

That was a bit of a full circle answer :)