I am looking for a low cost builder, and need to stay around 85-90 PSF exclusive of utilities.

Anyway it is extremely laudable that you took such a bold plunge into real estate investing without the relevant experience, not a major issue though as there are many here that would be willing to guide you. 

I am looking for a low cost builder, and need to stay around 85-90 PSF exclusive of utilities.

BP is a great resource, and you will find a lot of seasoned investor willing to help and guide you.

I know this doesn't necessarily answer your question but I hope it provides a guide in the right direction for you.

my price range is max 150,000 looking for someone to show me the best areas to invest and stay away from

There is a 1/2 bathroom in the basement that i will like to do as well as long as it stays under my budget. 

I have noticed whilst reading some of the articles and guides on here that some of the situations and examples don't really fit how New Zealand works, however I still don't know a whole lot about how New Zealand works either.

I try to stay away from the larger property managers and focus on the small landlords who are going through an eviction.  

Feel free to message me if it needs to stay private.