New Zealand is not among the cheapest countries. The country has one of the highest minimum wages but the higher wages equal higher prices. The cost of living in New Zealand varies considerably depending on your expectations and your standard of living. You can rent a house and eat in restaurants, or you can stay in your car and stock up with a pack of Chinese noodles. And of course, anything in between.
In any case, if you are going with a Working Holidays visa, you may already know that you should be able to show them that you have on your account at least 4,200 NZD per person (may vary depending on the country you are from). Checks on the account balance are random and are done as part of an immigration check at the airport after arrival. If you do not prove that you have sufficient money on your account, you are violating the conditions for granting the visa and you do not have to be allowed to enter the country.
We really recommend that you keep this minimum. You will have peace of mind at the beginning of your journey. If you are looking for a job, you will have the opportunity to choose and not be forced to do the first one that comes up. If you plan to buy a car after your arrival, count the amount for the minimum required amount, so it is better to buy a car for more people.
Count your estimated costs before the trip and make sure you have enough money to cover it. If you want to buy a car, prices range from NZD 2,000 for a very old car up to about NZD 10,000 for a luxury fully-equipped self-contained van. Average prices range between $ 3-5 thousand.
You also need to account for housing to the beginning, meaning a cost of about 300 - 500 NZD per person per week. It is generally better to be prepared for the worse and more expensive option and be pleasantly surprised, than not being prepared at all.
It is also good to consider having some credit card or debit credit in your bank - just in case.
To avoid carrying too much cash with you, it is possible to use advantageous money transfer services. Faster and cheaper than International Bank Transfer is CurrencyFair and TransferWise.
More about the topic is written in the Money Transfers article.