iSUBSCRiBE are offering a fathers day promotion that gives you a 20% off code for BookDepository.com after completing a order with iSUBSCRiBE, typically you see 10% off BD so a 20% saving is decent even if it costs $1.
Subscribe or renew any magazine subscription with iSUBSCRiBE before 14th September and you'll receive bonus discount vouchers from Hotel Quickly, Canningvale and Book Depository.
Book Depository conditions
1. Offer valid for redemption from 12th August 2015 to 30th September 2015.
2. Coupon code can only be used once and is valid in New Zealand only.
3. Offer is only valid if you enter the website at www.bookdepository.com/isubscribe-NZ.
4. Coupon codes cannot be used in conjunction with any other voucher or coupon.
While the site says it's for subscriptions you still get the discount for making an order of a single issue of a publication.
Get the $5 off discount by signing up to the newsletter
https://www.isubscribe.co.nz/newsletter.cfm
Purchase this $6 item for $1 after the discount is applied(only via credit card, no paypal)
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 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.
BD coupon expires on the 30th if anyone else got in on the deal.