Purina offers a bag of its Purina Tidy Cats Pure Nature Cat Litter for $0 via this online rebate. (You must upload your original receipt with the purchase circled. A mail-in option is also available.) That's the best rebate offer we've seen on this cat litter. It's valid only on 7.5-, 12-, or 14-lb. bags. (Walmart stores currently charge $12.78 for a 12-lb bag.) Rebate is limited to one per household and ends May 12, 2015.