I just built a new system in NZ, but I didn't need a monitor or OS. Ya, a decent build on that budget will be a challenge.
I recommend using nz.pcpartpicker.com to set up the build and ensure compatibility, but price all or some of the parts from ebay. I found ebay, even with high shipping costs to NZ, still cheaper than most NZ retailers. As with anything, the more time and research you do, the better prices you'll find. Good luck!