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