I have traveled to New Zealand aprox. 15 times over the last 30 years. I usually take $110 US with me and a credit card.I convert the 100 to NZ dollars when I arrive. For the last 12 years or so I use an ATM card for money, but mainly use the credit card.
I think it is Australia you do need to prove funds if you are entering the country on certain visas or for certain durations, but not New Zealand when i last checked.
I am from the UK and was in NZ a few years back and was not asked for proof of funds, but was only going for 1 month. I would double check with the NZ Consulate/Embassy before you head off as it may depend on the duration of your intended stay with out working to obtain funds you may need to prove you can afford to look after yourself without working.