Prior to our departure, i have arranged with a buyer from Trademe to confirm a car. She was so nice to agree and we did the handover at the airport, thus saving me some money on car rental, which would have cost around $300 for 4 days.
Trademe is a very popular online marketplace portal in New Zealand. You can find close to everything, including cars, houses for rent/sale and even second hand furnitures. One of the downside is that you will need to have a NZ residential address and contact number. It does not accept oversea users to register an account.