How is New Zealand able to provide prices that are so much lower than the USA?
Having a total population of only 4 million, the New Zealand economy is much smaller and more geographically isolated than the USA with lower wage costs. 
There are two medical systems in New Zealand; a publicly funded system which is essentially free to New Zealand residents and a private system for those who don't wish to wait and are willing to pay. The effect of the health insurance industry on the medical system is therefore less prevalent than in the USA, with market prices being led by the biggest funder of health care, the New Zealand Government.
In addition to this the private hospital system in New Zealand only treats non-acute arranged surgical patients. It does not have to cope with (or need the infrastructure for) trauma and chronic conditions, which are handled by the parallel public system. As a result the costs for running a private hospital are much less.
The New Zealand medical system runs on a "non tort" basis, with the Government covering most malpractice and medical accidents through the Accident Compensation scheme (ACC). ACC pays out more often and more appropriately than in the USA for rehabilitation and to correct genuine mistakes or accidents. It does not pay vast, lottery like sums and as a result malpractice insurance is dramatically less expensive, even though the chance of the patient receiving costs for rehabilitation and time off work is much higher.
Find out more about package costs from Medtral New Zealand.