The South Island is beautiful. So is the North Island, but speaking as someone who comes from a colder climate, I have to say that parts of the North Island were simply too rainy for me. I have recently moved down to Christchurch and am loving it so far, despite the cooler temperatures. The trick is to get a comfortable house with heating, which you will pay for here, but which is worth it.

We looked at some places for $300/week that were small, old, unmaintained, and cold. We got a place for $325/week that is old but large enough for two-4 people, updated, maintained, and warm. I don't know about prices in other areas, but you can always look on the trademe website for some ideas of what is being offered and for how much.