If you're flying into AKL don't be afraid to look into Happy Campers either (they will pick you up from the airport too). Have used them a couple of times. Diesel high top Hi-Ace camper for 10 days with unlimited kms only cost me $800NZD (plus $68 in diesel rebate tax). Top 10 Caravan Park (equiv of our Big4- but heaps better) in Roto is nice & central to everything & charge $36NZD per night for a powered site- amazing amenities & a hot mineral pool to soak the muscles in after every ride. 20min ride or 8min drive to Whakarawerawa. You're also then a free agent to see, ride & do whatever you like- you can free-camp almost anywhere in NZ, so long as you've got a portable toilet (legal requirement in NZ if free-camping) which was only an extra $15NZD & is available with your vehicle hire from Happy Camper.