Living Expenses

The cost of living differs between cities in New Zealand. However, approximate living costs are

Homestay fees are $230 (2019/20) per week.

If you are in a homestay, you may spend about $100 per week on lunches during the week, bus fares, entertainment etc.

Flats / Apartments
Average prices for flatmate positions range from $70 to $120 per week (+ expenses), and average rent for houses starts from about $200 per week (3 bedrooms, unfurnished).
If you are living alone, you may spend about:

Electricity:$30 per week (summer); $45 per week (winter)
Telephone:$15 per week
Bus fares:$25 per week
Food:$100 per week
Total:$170 per week (summer); $185 per week (winter)

If you are sharing, you may spend about:

Electricity:$15 per week (summer); $25 per week (winter)
Telephone:$8 per week
Bus fares:$25 per week
Food:$80 per week
Total:$128 per week (summer); $138 per week (winter)

A lot more information about this can be found at this link.