With 3 Kg Optimum cat food bags (& Aldi's larger $1.99 cans of tuna), we have dropped the annual cost of Cat Food a lot.
In case your cat's picky, we pivoted one cat to "Furball with Chicken" (from "Adult"…?) without issue. :-)
I'm reliably advised that - across Coles (in SA) - there are significantly more than 10 3Kg bags available.
PS How come Optimum's Dog Foods are SO MUCH CHEAPER than Cat Food?!?
"Grain-heavy, by-products, nasty digests."
http://www.petfoodreviews.com.au/dry-cat-food/optimum/