Wishbone Cat Kibble Roost 9.1kg $45.99 (Usually $57.99) @ Costco (Membership Required)

I hear good things about this cat food brand and by far this is the cheapest I've found for something this size in a long time.

Countdown seems to sell the 1.8kg bag for $19.99.

Here's the link to their other specials, but the cat food is a good one. Valid until the end of the month or when they run out (and we know how painful it is to get that back in stock).