If you want full time web dev work, Auckland and Wellington are really your main options. Cost of living in NZ is high (relative to salaries), but for most people the pace and quality of life make up for it.

Given that NZ timezone is only 3-5 hrs difference from the west coast of the US, I personally would look for remote work for a US company while living in NZ (salaries and the exchange rate would be strongly in your favor). However, if you need a visa sponsorship this wouldn't be feasible.