Our local stores sell windows xp home edition for $100 and 1 gig of used ram for $150. So I think local stores are out of the question.
I don't mean the local PC shop that is part of some chain, I mean a hardware dealer somewhere in NZ. Just looking at Google there are sites like
this,
this,
this and
this that you possibly source from.
For some comparisons, take for example an i7-6700K. I got mine for $519AUD, which converts to about $550NZD, and on the alphacity site you can get it for about $570NZD including GST. Or you could look at memory like you suggested. I can't find the exact model of memory I have, but this one is similar, so a pair of DDR4 Ripjaws 2400Mhz from the pbtech site goes for $194.35NZD which includes GST. I'd be spending $189AUD from the store I get my parts from, so $200NZD on those, so you're getting a better deal than me there.
I know the parts can be sourced elsewhere overseas cheaper, but like sm said, if something goes wrong, easier to deal with someone in your own country than half way across the world. Better still if you get the components from the same place, they come together, not days/weeks apart. And then also, I personally like to support the local stores than the overseas markets putting everyone out of jobs.