I have no idea why these are so cheap as last time I purchased them for the wife they were $20 or so for a 4 pack. These are not marked as clearance items either.
I'm personally not a fan of cider but these seem to get good reviews.
Liquorland sell a carton of the bottles for over $110 and first choice $113
BWS also have the 4 x packs for $10 and the cartons for $55
https://bws.com.au/product/85296/zeffer-apple-crumble-cider-…
Imho they're cheap because they're yuck. Vinegary.