One of the sale items at SunMart are Pillsbury Cake and brownie mixes 10/$10 (you get them for $1 each even if you don't buy 10). They are regularly $1.95. The sale runs through Saturday 6/6.
I usually buy a few when they are on sale to have on hand. Since it is just me, sometimes I bake up something and freeze the extras.
One cookbook I like is the Cake Mix Doctor by Anne Byrn. Her other cookbooks are Chocolate Cake Doctor, The Dinner Doctor, Cupcakes Cake Doctor and What Can I Bring Cookbook.
The Cake Mix Doctor has recipes to spruce up ordinary cake mixes that taste more like scratch with simple ingredients.
When using cake mixes its easy to add ingredients to them to make a change. A couple weeks ago, I had a white cake mix and a can of cranberry sauce. I made the cake as usual and added the cranberries. The other night I mixed up a chocolate cake mix per directions. I filled muffin tins a little under 1/2 with the mix. Then I mixed a block the cream cheese with some mint flavoring and a little powdered sugar. I put a spoon full of this mixture in each cup. Then I put another layer of the cake mix. And baked as usual.
So one tip to save money is to try to buy items you use regularly when they are on sale. And using items you have on hand. Sometimes you can substitute things for other things that you have on hand.