Eggs are fairly cheap and healthy, depending on how you eat them. Anything you make yourself will be cheaper than mass-produced stuff.
Tuna is cheap.
Cheapest meal with the most "bang" for your buck will probably be: whole grain pasta, frozen vegetables, half gallon of skim or 1% milk, oatmeal, butter, eggs, tomato sauce, and chicken legs/thigh meat (or stewing beef), cheese, whole grain bread, peanut butter, honey, tuna, mayo, and frozen fruit.
Right there will give you approximately two weeks of breakfasts, lunches, and dinners. You can make smoothies, oatmeal w/fruit, omelets, chicken w/pasta and veg or chicken w/veg, and either pb & honey or tuna sandwiches (for a single person). You can also use the peanut butter as part of your pasta dish if you want a peanut thai flavor.