The price for fuel in New Zealand varies throughout the country.
The current prices for petrol is around $2.30, diesel costs around $1.65 per liter. In remote areas petrol stations might be difficult to find and prices can be a significantly higher. It is recommended to fill up the tank whenever you pass bigger towns.
In addition to the diesel price there are "Road User Charges" (RUC), the diesel tax which is charged 6.20NZD (6.80NZD for Euro Familia 5 and Budgy Familia 6) per 100 kilometres.