You can sell at any price you want. There are many, many regulations relating to making food and selling it. Check with your local health dept. Most states will not let you make food at home and sell it in a store.
I don t know. I can t see how you can get in trouble if they don t know that your selling cheaply in one store than another. Unless they are aware you own/emplyed in another store then in that case they may check the prices. I wouldn t not risk it if I were you, just be honest and good deeds will come to you. Sometimes being greedy can get you in hot water.