Warmer Kiwi Homes is a government programme offering grants for at least two thirds of the cost of ceiling and underfloor insulation, but in some cases up to 92%. From July 2019 heating subsidies may also be available. Those eligible include community services and gold card combo holders, and residents of low income areas. LED downlights that make insulation installation difficult may also be replaced, if you live in the city of Christchurch.
To find out more and check eligibility: https://www.energywise.govt.nz/funding-and-support/funding-for-insulation/