In reply to George Fisher:
Prices do vary a lot but are generally expensive.
7days isn't very long are you sure you definitely want a camper van? It would be cheaper to hire a car and stay in motels... or holiday parks have cabins if you want to live the camping lifestyle.
Having said that, we hired a camper to move house from Auckland to Dunedin in October/November.
We used Budget Campers, which were considerably cheaper (about 150NZD per day but October is out of season). They were fine, a bit rough around the edges as you would expect for a 1998 camper done >500K km. Perfectly comfortable enough though with loads of space for the 3of us and our belongings. It took us 2800km including some rough terrain up to Lake Waikaremoana.
It had the same equipment as a new Britz/Tui/Maui/Apollo etc (Budget is owned by Tui) just slightly older.
Anyway, happy to provide further info if needed/desired.
Good luck and happy travels!