If you're looking for cheap yet fairly healthy, I've been on a pretty steady diet of:
Breakfast:
-Oatmeal, quick oats, not the fancy stuff. With Brown Sugar and Raisins for flavor.
-Milk or occassionally juice.
Lunch:
-PB&J
-Yogurt
-Apple, Banana
-Pretzels
Dinner:
-1/2 lb. pasta
-Shredded cheese for flavor
-2-3 servings Frozen or canned veggies (I prefer canned black beans or fresh peas mixed in with the pasta)
-Chicken or Fish 2-3 times/ week
Snacks:
-Sugary cereal with milk for carbs
I've been able to keep this right around $20-$25/ week. A smidgen redundant, but I know exactly how my body will react , and my trips away from my cubicle are like clockwork.