JQNZ F/O is $127K per year as year 1, overtime paid at about $155 per hour if you fly over 65 hours per month. Expect between $10K-$20K a year before tax, depending on how much you want to work. Expect about $1000 a month tax free allowances.
There are busy months and there are quieter months, you do get enough sleep and most pilots in NZ are happy to stay, some look at other options, but no more than any other airline.