If you use something like skyscanner you'll see that routing via Sydney or Brisbane will give you a lot more options. The additional competition from having other airlines such as Virgin AU and Delta makes the flights generally cheaper. I've done this before and at the time the cost saving was significant enough to offset the inconvenience of the 3 hour additional flight in the wrong direction.
From November (I think?) Air NZ will be flying direct from Chicago to AKL, otherwise the options are West coast (SFO, LAX and Vancouver) and Houston.
If you do look at flights that are not direct from the USA to AKL, do check the total journey time. Anything with overly long connections or routing via Asia, I would rule out.
If you are looking at Air NZ, make sure you also check www.airnz.co.nz as opposed to the .com version when looking at domestic and trans-Tasman flights. Jetstar is the other domestic carrier (a bit more budget and considered a bit more unreliable).
The flights prices do fluctuate wildly, and there is normally at least one airline offering specials. Might be worth getting a fare type that will allow date changes on the return flight without extortionate fees.