Last time I checked with the powerswitch Flick Electric was the cheapest:
https://www.powerswitch.org.nz/powerswitch
Get $75 cash deposited into your nominated account after being with flick for 3 months.
https://www.flickelectric.co.nz/
Terms and conditions:
Must apply before 30 June and have power switched by 31 July
https://www.flickelectric.co.nz/terms/promo_terms/