Hey sweet heart, why don't you try a regular recipe instead of a cake mix?
1. It's probably going to get more puffy and tasty. Good for your selling.
2. It's cheaper than cake mixes. Even better for your class/stuff funding.
Don't be afraid: if you already have a nice oven, all you need now is a spoon and willingness
Check out some recipes in the web. I can even send you some...