Don't worry anymore, I have acquired a suitable unit. For closure and those who may be in a similar situation, the unit I got is the AquaFX Barracuda RO/DI unit (50 GPD) from Amazon US. Got it for $388 NZD (this price included shipping and a handheld TDS meter). I tried to find a suitable option here in NZ, but it was all way too expensive for my budget. The unit seems to be good, heaps of protective foam packaging and took about 1 week from order placement to arrive. Will test it when my TDS meter arrives (it was shipped separately).