Please any suggestions for cat litter on a budget with 4 FAT cats that use JUMBO BOXES (I'm talking 10.5 - 19 pound cats). One of them has occasional bouts of asthma so I have been doing well with Dr. Elsey Respiratory Relief, but I see it has now gone up to more than $ 14.00 for the 20 lb box. My "system" has been to wash pans and do full litter replacement monthly, but I still go through a LOT (I scoop every chance I get). Would non-clumping be more economical even though I would be changing the boxes more? Dust is an issue for my asthmatic boy, so I can't go super cheap.