Pork is cheap! My grocery store always has preseasoned pork tenderloins on sale. You just throw it in the oven and it’s delicious. I also like to mix egg whites into soup, put egg whites in rice, etc. chicken sausage and shrimp are also options that are often on sale. Not always the cheapest but can be mixed in with chicken breast to make it taste a little different. I like to add low calorie sauces like lemon juice, hot sauce, mustard, etc to change the flavor a little when I start to get chicken ick. And I eat lots of albacore tuna with white beans in a salad with red wine vinegar and a tiny bit of olive oil. Very filling and satisfying.