Short answer: Discharge fee ~$150-$400. Lawyer fee to register discharge. Then you own the house outright.
When you pay off your mortgage, the bank charges a discharge fee to remove their claim on your property. It is usually $150-$400. Your lawyer also charges to register the discharge. The bank gives you a discharge authority. Your lawyer files it with Land Information New Zealand. Then you own the house free and clear.
Bank Discharge Fee: $250
Lawyer Fee: $300
Total Cost: $550
Result: Clean title, no mortgage