Cook all your meals in advance. Pasta, potato gem casserole, and a Thai red curry can give you roughly two weeks of lunches and dinners if you alternate well. You can add breakfast bowls of eggs, cubed ham, and potatoes and they’ll keep for a week, minimum (I don’t know how long exactly because a dozen eggs gets me six meals).
I usually pay around $50 every two weeks for food, plus a bit more if I’m running low on coffee or milk.