This might be another amazon au pricing error or listing error. I stumbled across this while trying to use the credit given from the dishwashing tablet pricing error from amazon au. The listing says its for a pack of 20? Unsure if this is accurate or not. If it is, $20 for 20x 64gb micro sd cards is an absolute steal. If it is another error, they might give us more credit for having incompetent website editors.
If inappropriate, please delete. Thanks.
Edit: the SanDisk 64gb cards don't seem to add to cart anymore. Try using one of the other ones listed in the comments, or just try to find another "pack of 20" item if you wish to join the 'amazon's headache party' .