Got this email last night. I'm an Audible US member. Not sure if it applies to AU.
Audible Members' Sale - 50% off All Books
30
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Apparently this is 50% off the regular price, not the member price which is already a 30% discount (even though you need to be a member to access the sale). So really it's a 28% discount on the member price. That means that for many items, credits will still be cheaper - though this may be good for some cheaper titles.
With 50 % off. These audio books are still overpriced.