Start with oatmeal ( I buy the five minute kind which is tastier) for breakfast sprinkled with a few chopped walnuts and raisins and perhaps a little honey.
For lunch make a big Greek salad with your favourite lettuce, a slice of low fat Feta cheese, half a sweet onion, five black olives, two or three plum tomatoes ( which are cheaper) with oil and vinegar. Or take out the Feta and make it a Niçoise with the same ingredients plus half a can of tuna fish and a red pepper.
For dinner make a small quantity of spaghetti and accompany it with lots of fresh sauce made with a few tablespoons of olive oil, chopped sweet onion, garlic, four or five plum tomatoes and many mushrooms. You can add black olives and capers if you like and a sprinkle of oregano, thyme, or basil to taste. Or just make spaghetti ( keep the quantities low for the starch) with a can of tuna crushed with the juice of one lemon and lots of cooked vegetables thrown in. You can add asparagus cut up into pieces or green beans or even broccoli.
Another wonderful, cheap and low calorie dinner dish for the summer which a French friend from Marseille taught me to make is ratatouille. This is best made on a day when you can be at home to stir occasionally as ideally it should cook all through the day until the vegetables have turned into a thick sort of paste. You can make a huge pot ( double all the ingredients) and eat it for several days.