We traveled around New Zealand for three month a year ago, Nov -Feb, and used Top Ten Holiday parks for about 75 % of our stays. Although we stayed in the Motel and cabin units, fully self contained and located in holiday locations, beaches, mountains, lake etc.. The do range from 80 dollars to 150 dollars a night. More expensive in December and January, remember December is their July here. The holiday parks have accomadations from tent sites, to RVsites, to dormitories and flats with just a bed, to full units with kitchens and ensuites.
The way we travel NZ is to fly in, rent a car or SUV, and travel with no reservations and staying where we like. After two trips there, one for six weeks, and the last for three months, it is the way to go. Remember, the roads there are like driving the Beartooth Highway all day. (That is a winding road up and over the mountains going into Yellowstone Park) So I don't want to drive one of the rental RV'S they are famous for. Plus there is no "free camping" in NZ.
We will probably winter there next year again.