It's a bit late replying, sorry but I haven't been on for a while.
It cost me $700 for lenses for my own frames and $400 for a pair of glasses for an 8 year old 4 years ago.
So...
Get yourself an eye test and get a copy of the prescription (Specsavers will NOT give you a copy).
Then go here, they ship to NZ : -
http://www.zennioptical.com/

Cheers
G