Amazon is a monoculture. Broaden your sources to allow for healthy competition.
Smaller Booksellers
The Book Depository ships to NZ, has over 20 million books and free delivery worldwide. Website 
Free Book Sources
Just because it's free doesn't mean it isn't good. Here's a list of places you can find free reading material.
The Internet Archive Books collection. Website
Books that have entered the public domain are available on Project Gutenburg. Search
Global Grey's free ebooks in
PDF, epub, and Kindle formats. Website
Tips
Lifehacker's "How to Buy Ebooks From Anywhere and Still Read Them All in One Place". Lifehacker
Bookbub notifies you when there are deals on books that are on your wishlist. Website