Sadly we use the big cheapest 40 pound box of litter from Walmart. When you have as many cats as we do it is all you can afford.
However we do get them decent cat food. Since Owen was hospitalized we had to put all our kitties on the Catkins diet switching to the urinary track cat food.
I don't know how much the Walmart kind costs, but the Petco refills are $10/35 lb., which is cheaper than Tidy Cats (which I used to use, as well). So it might be worth a look!
Yeah it's so hard when one has a special diet ...Yuan and Maggie both eat the allergy-safe wet food, but they have different kibbles, and they are always stealing each other's. But too much of either in the wrong cat makes them barf or have the poops. Sigh! I need those bowls that only open for the right cat, but of course they're $150 each! Maybe if I become a crypto millionaire. LOL