Amazon has the 37-lbs Fresh Step Clumping Cat Litter (Two 18.3lb boxes) for $27.50 - 35% off coupon (check "Save an extra" box, eligible on first S&S order for this product) - 5% off with Subscribe & Save (can cancel anytime) = $16 with free shipping on $35+ or with Prime. Roughly 44 cents per pound. 

• The 37lb multicat option is $17 after coupon, S&S.