Compact Flash cards are light and small. The shipping costs can only be negligible.
If you buy a 256Gb Sandisk Extreme Pro from B&H in NYC it costs the equivalent of NZ$813
The same card from a NZ retailer is NZ$1,800!
How is it possible to explain a differential that size? It certainly isn't GST.
I never buy either CF or SD cards in NZ now as they are invariably cheaper overseas regardless of the capacity. With discrepancies this large, I am surprised they ever sell any at all through official channels here.