Here are the prices you see if you access the Kiwi Rail website from Chrome in the US:
Note the blank space between the trip name and the prices. What could be there? Google “Kiwi Rail discounts” and find information that suggests accessing the Kiwi Rail website via a browser with a New Zealand IP address. When you do that, you find:
Why are people physically in New Zealand getting better deals? You can tell a demand elasticity story: New Zealanders have cars and access the website from browsers with NZ IP addresses. Their demand is more elastic than that of foreign tourists. So, price lower to people buying from NZ. You can tell the reverse story: Many tourists in NZ buy when there. Their outside option is flying and buying flights late is expensive. Tourists make up the vast majority of train travellers in NZ. People buying from abroad are also tourists but they are buying early and can find cheaper domestic flights. So their demand is elastic.So price high for people buying from NZ IP addresses but low for people buying from foreign IP addresses.
Whatever the truth of the matter, it is quite interesting to see this kind of price discrimination by Kiwi Rail. God knows what Amazon is doing in comparison!