Its good you've chosen not to buy parts from nz stores, you really, really get shafted on pricing as you know
if you are assuming you can run straight into a wrecker w/o checking first, go in NOW and check - else you may be unpleasantly surprised at either A) the prices or B) the availability of the core you specifically want; they can be pretty difficult to get hold of. You seem fairly certain though so it sounds like you may have the rad already - if so, disregard.
The storm G4 is available through swiftech now, for 75ishUSD - so you wont be spending too much more on the block if you choose to go in that direction.
If you want to save possible headaches, grab a metre or two of clearflex whilst you're there - tubing in NZ is non-existant.