Only valid on the audible.com site but works with an Australian account, coupon expires two months after date of issue.
Members that aren't on a plan should get a slight discount if you add any audiobook through Amazon.
For example Ender's Game Alive: The Full Cast Audioplayis $11.95 vs $19.95 direct. Once you add one audiobook through Amazon, you should see different prices (they generally end in a 5). I found a few that were more expensive so compare with a different browser or private tab/window.
Also if you're trying to qualify for the April is Listening Month $10 coupon, Aladdin and the Enchanted Lamp and Gulliver's Travels free whispersync pairs count towards the total.
I recommend divergent series or goldfinch