Enough so that you can keep all the litter boxes filled with 3-4 inches of litter, and scooped twice a day. What I spend will be different than another person. I have 4 cats, and need to use the more-expensive light weight litter as I have a weight restriction in my lifting, and can't heft the 20 pound jugs nor 35 pound buckets anymore. Boxes also need to be periodically dumped of all litter, scrubbed, and filled with fresh. One cat will use less litter than two, two less than three, and so on. Quality litters perform better than cheap ones, and are more economical to use.