Amazon has a 40% S&S coupon on many various litter products including litter boxes and other various litter products. Browse the litter category to see more. If people could add to the list that would be great.
Link to 40 lb. Dr. Elsey’s Ultra Premium Clumping Cat Litter:
https://amazon.com/gp/product/B0009X29WK/
Note: You can only use the coupon once on one item, so use it wisely!