Imoova lists all the campervans and cars that are need re-positioning in NZ. I did one of these in Australia from Cairns to Melbourne (flew to Cairns to meet friend) a few years ago and it worked out fairly cheap. Only downside is the cost of petrol which is killer in these big vehicles. Best value is getting the ferry for free.
We've done quite a few of these relocations thru imoova and can highly recommend! Only sign up to the deals with free ferry, otherwise you're up for $350 extra costs for ferry costs!