iSUBSCRiBE are offering a xmas promotion that gives you a 20% off code for BookDepository.com after completing a order, typically you see 10% off BD so a 20% saving is decent even if it costs $1.
Book Depository conditions
1. Coupon code can only be used once and is valid in New Zealand only.
2. Offer is only valid if you enter the website at www.bookdepository.com/isubscribe-nz.
3. Coupon codes cannot be used in conjunction with any other voucher or coupon.
4. Coupon codes are non-transferable and cannot be exchanged for cash.
5. Coupon codes can only be used at time of purchase and cannot be applied retrospectively.
6. The Book Depository Limited retains the right to end this promotion without notice.
7. Offer expires 31st January 2016.
Expiry: 31st January 2016. Terms & conditions apply, to view visit www.bookdepository.com/isubscribe-nz
Get the $5 off discount by signing up to the newsletter
https://www.isubscribe.co.nz/newsletter.cfm
Purchase the $6 item for $1 after the discount is applied
https://www.isubscribe.co.nz/The-Art-Of-Preserving.cfm
You get the coupon code when the order is completed
It's also worth checking on a site like Booku(booko.com.au) if your books can be purchased cheaper at other major online retailers, it factors in shipping etc(to AUS) and should be close to NZ costs.