The best option to eat in New Zealand is definitely Asian cuisine. Everywhere there are Indian, Thai, Japanese, noodle bar, restaurants etc.. The Shiraz is a cozy restaurant that serves midday menus where for 5 euros you get, curry, naan, tandoori, and all kinds of Indian dishes, both vegetarian and non-vegetarian.
A Thai restaurant that has a cheap fixed lunch menu for about 5 € and in any case lunch or dinner cost around 7 euros. I Highly Recommend the Chiang Mais style noodles soup with coconut milk, that has a slightly spicy flavor and fabulous aroma.
It's a rustic cafe within a facility dedicated to selling rural and rustic DIY items and decorations. I guess they have to attract customers because the prices are quite low. While you're eating or having a coffee you can think about your garden.
The restaurant is attached to the dive center, so in the morning it's very busy serving breakfast before you go diving. At noon they offer varied menus and the terrace is very nice with a barge converted into a chill-out area.
A small shop run by a Chinese family, it's the only one that's open 7 days a week in Whangarei. It specializes in roasted chicken both, like a lamb, or beef, and some chinese dishes. They have fixed menus starting at € 3.