This is possibly more for the people feeding community cats/strays or fostering. And this can be sending a mixed message, obviously lower quality dry food has the risk of health issues/emergencies like blocked bladder when feeding for an extended time.
But if you’re needing to feed multiple pets on a budget and can afford to pay the cost upfront, it’s possible to save a lot of money by buying in bulk. (Note - if it doesn’t get used up very fast you might want to consider keeping it in a plastic or metal bin or tub with a lid and putting a moisture absorber in there. So mice don’t chew their way in and it doesn’t go mouldy.)
The lowest end can be around $30ish for 8kg of Moggybix or $34 for 20kg of Eureka. It’s much higher for premium and prices keep getting hiked but sizes vary and the unit cost can be lower than half or even a fraction.
As always shop around and compare as some deals aren’t the best. Watch sales and use reward programs or discount codes too.
https://www.costco.com.au/Grocery-Household/Pet-Supplies/Cat-Food/c/cos_18.7.2
https://www.petcircle.com.au/cat/food/bulk?sort_by=once-off-price&sort_order=ascending
https://www.bunnings.com.au/products/pet-supplies/cats/cat-food
https://www.salce.com.au/ (Wholesale, bulk cat and dog food not showing but check back I guess)
https://www.petstock.com.au/products/eureka-bulk-up-20kg-1-variant-141216000232 (currently out of stock but check back)
https://www.bestproductsaustralia.com/dry-food-cat-bulk
For stray cat desexing check out a targeted desexing program through your council if a grant has been received, or Give A Kitty A Home.