Here is a link to the Auckland University Underwater Club AOW page: http://akunidive.com/padi-advanced-open-water/
$545 and likely including accommodation / food (if 8 or more are on the course - from what I read on the page ...
Google turned up a course for $495 but I would imagine any accommodation is on top of this? (Looks like they dive the wreck of the Waikato which would probably mean at least a nights accommodation if you are Auckland based). http://kiwiscubadivers.co.nz/advanced-open-water-course.php
And for comparison there is Goat Island Dives AOW (again I found this via Google search) http://www.goatislanddive.co.nz/advanced-open-water-course
$549 but if you live in Auckland then there shouldn't be accommodation costs.
Personally, if I were in your shoes I would be considering Northland Dive through the Auckland University Underwater Club. AUUC has a history of being cost focused (what students aren't?) and having a lot of fun at the same time.
(Disclaimer: I was heavily involved in the AUUC in the '80s and president in 1988 so I may have a slight bias