Ghetto pizzas. Make some toast put tomato sauce or ketchup on it then sprinkle with cheese. You can nuke it to melt the cheese or if you want to spend more effort pop it in the oven. Also if you have more than 2$ you can put toppings like veggies and pepperoni on it.
Edit I just remembered another poorman meal I used to eat all the time. Boil ramen and strain. Add tomato sauce and cheddar. It’s like really shitty spaghettios or regrettios if you will. Cheap filling and full of sodium