Buying or renting a car in New Zealand
This article is a travel topic
Driving in New Zealand is a great activity which, not surprisingly, requires a car. This article discusses some ideas for acquiring a car in New Zealand if you don't already have one. It is edited from the excellent article already up on Buying or renting a car in Australia
Buy, Rent or Buy Back?
Car Rental in NZ is not too expensive, but the general guideline is that if your trip is longer than about 8 weeks, it is worth buying instead. Remember that you probably need about a week at either end of your trip for buying and selling. You will also need to pay for insurance (not compulsory but a VERY good idea), AA membership (ditto), registration/warrant of fitness (if applicable) and any fixes. So it can be a gamble to buy.
New Zealand is not very big and the ins and outs of travellers do affect the market. Cars are pricier and scarcer in October/November, and cheaper/more common in March/April, matching when most travellers arrive and leave. That said, I've now owned four New Zealand cars bought and sold at these times, and never lost more than $200 each time. Actually made a profit on one car!
Another option is to buy a car with a buy back car guarantee. This basically means that you buy and own the car but when you have finished your trip you will get a guaranteed price back from the dealer that you bought it form. The percentages vary between companies but it usually is between 40 and 60 per cent depending on the length of time you have the car for. These can work particularly well for people who don't have enough time to sell or don't want to waste their time selling on their holiday.
Tips for renting in New Zealand
You can rent a car in New Zealand if:
Requirements for cars; many backpackers go for a station wagon as they are planning to sleep in it to save money on accommodation. Before you do this, remember: New Zealand has an excellent network of inexpensive hostels and campsites, and also one major crime problem: theft from cars. A 'saloon' with a secure boot which hides all your possessions will be much safer for your kit. Also be aware that hostel owners don't generally like you sleeping in the car outside and expecting to use the hostel showers etc, as this will overload the place.
Tips for buying
The best tip is to check the car legally, and mechanically before you buy. The legal check or VIR checks the legal history of the car which includes ownership history, police interest and security interests registered against the car. In New Zealand these things can all carry problems to the new owners and can result in you losing the car and therefore your money. The mechanical check should be carried out by a mechanical company it can also be called a pre-purchase inspection. Most reputable mechanics will perform such checks for you, and they normally cost between 100 and 160 dollars depending on the company and the quality of the check, they should take around 2 hours.
Many of these tips are true regardless of where you are looking to buy a car, but there are a few concerns specific to cars in New Zealand that you should be aware of.
'New Zealand New'
This concept needs some explaining. New Zealand imports many Japanese cars; the Japanese roadworthy requirements are so stringent that it may not be worth fixing a car that is only a few years old, so off it goes to NZ. Cars in Japan can have a hard life, so ideally you want a car that came straight to NZ and didn't drive round Tokyo first. To tell which is which, look at the dates on the registration sticker; it will show the year of the car and a smaller month and year. If these are the same, the car is NZ new; if not (e.g. '1990 Toyota Corona' with a date of 11/95') the car has spent five years in Japan first. Not necessarily a no-go, but be aware. The locals much prefer NZ new.
You should do do both a legal and mechanical check before you buy. When it comes to selling, don't give away your flight date; if it is tomorrow they will smell the desperation and you'll be lucky to get $100 for the car. A good answer to 'when are you flying?' is 'when I sell the car'. Check for reviews of the place you want to buy or sell. Know the value of cars in New Zealand - do your research first - and don't be persuaded to go above what you know is the market price by the market proprietor - they may not be acting in your best interest.
Auckland has several car markets, the main one is on Sunday at Ellerslie Racecourse. Sellers $20, free to buyers. Turn up before 9AM if you can, it will all be finished by 12. Onsite registration transfer and mechanical inspections. Christchurch's similar operation is at Christchurch's Addington Raceway on Sunday from 9AM.
The Backpackers Car Market  Centrally located in Auckland and Christchurch and open everyday between 9.30 and 5pm. Its the only dedicated backpackers or travelers car market in Auckland.
The Christchurch Car Market  located in the city open everyday from 9am until 5pm. They also have a mechanical work shop, which can come in very handy when buying a cheap car as it can be checked on site and repaired if needed. 236 St Asaph Street city centre.
A2B Car Rentals. 10 locations throughout NZ with budget models starting from just $19 per day.
Airport Rentals. Late model rental cars, vans, minibuses & 4WD station wagons for hire at Christchurch airport. 
Crazy Car Hire NZ. Compare Car Rental from all the big names like Hertz, Avis, Budget & Jucy.
Hertz New Zealand. One of the biggest name is car rental all across the world. Locations at all major places in New Zealand.
New Zealand Rent A Car. They offer hassle-free car hire and great Kiwi service from popular locations throughout NZ
USAVE New Zealand. USAVE offer car and truck hire at all popular locations in New Zealand.
Due to natural disaster many of the Central Christchurch motor vehicle dealers and subsequent backpacker dealers have left the city centre and are now selling vehicles in the Addington and Hornby areas, which is a short bus ride from backpackers around the city.
Used vehicle sales websites
[] Bedmobils - Budget backpacker campervans hire + sale + buybacks. Excellent value.
[] buy-sell-exchange - This is online version of buy, sell & exchange weekly paper, what New Zealanders have used (and still do use) to buy and sell their things before trademe. Excellent for cheap wheels. Note that it is very likely that same car has been listed on both trademe and buysell due to both sites' popularity.
[] CarZonline - Offers quality new and used cars at discount wholesale / bargain prices. CarZonline is committed to find the best car deal in New Zealand.
[] - TradeMe This is a New Zealand auction site, like ebay. Its motor section covers all regions of NZ and you can arrange for pre-bidding inspection in all cases.
[] - Turners Car Auctions - Another NZ auction site, specializing in used vehicles. A tool is available to look up how much past vehicles have sold for.