There is a .50 off coupon for DH cake mix, you can find it at Hot Coupon World (HCW):
I don't think I've seen any coupons specifically just for DH mix (usually you have to buy the frosting too).
If you've never heard of HCW, they are a legitimate site where people submit Target coupons and HCW lists them all in one place.
WOW!! Thanks a lot! I usually shop Target for my DH and this is even better!
Glad I could help - I'm off to stop up today!