I work overnight shifts. On nights that I work, I eat the majority of my food for the day at work (~10 hour days, a half-hour break, and I can snack whenever throughout the night). I usually take some sort of leftover food (winter is the best, as we rotate through various filling crock pot meals such as chili, hearty soups, etc.). Other "main entree" staples I rotate through are: spaghetti, noodles with shredded Parmesan cheese, couscous with veggies, leftover pizza, various types of sandwiches. Then I bring a lot of snacks/mini-meals (pretzels, fruit, yogurt with frozen berries (berries from Costco), popcorn, protein shakes), basically so I have a large variety of choices, so as to avoid going to our sub-par cafeteria for overpriced, bland, unhealthy food. For extra excitement, I have crystal light packets I mix with the water I drink! :)
Total cost is pretty low (sorry, poor estimator), but significantly lower (and significantly tastier!) than buying food at the work cafeteria. And I actually eat healthier on nights that I work (vs nights I don't work), since my "rule" is I can eat everything I bring (generally mostly healthy foods), if I so choose, as long as I don't make the trek to the cafeteria.