Hi Mark and
to MoveToNZ.
That kind of salary sounds pretty good to me although, yes, you are right when you say the cost of living in Auckland is more expensive. You could always assess which area you'd be working in and try to find a house that's a bit outside the city and cheaper, if the commute isn't too difficult.
Rates of pay according to INZ although they appear to be from 2005.
For more up to date info you could scan down
here for some idea of salaries in the construction industry for NZ and OZ.