I got a $3 off coupon for the new Queen Creek Petsmart in the mail today for any dog food.
I googled science diet and found a coupon for $8/1 35 lb or larger. Click here for coupon. It will only let your print it once.
Stack the two coupons together for $11 off. The 40 lb food is around 31.99. Take off the $11 and that is $20.99 for a 40 lb bag of Science Diet. This is a great deal for me considering the that is the cost of the $20 lb bag at my vet.