Dieting isn't about cost so much as it is about quality of nutrition. Fats are necessary as they help you digest foods (contrary to what you'd believe). Calories and sugars, and refined carbs are the real enemy.
-Stay away from sugary foods like cake, candy, and breakfast cereals. These are not helping you, and never will.
-Fiber is not digestible, therefor you cannot gain weight from it. The more fiber in your diet, the more weight you lose naturally, and the better your metabolism becomes. Whole grains are a good friend, and vegetables are as well. I start every meal with a large salad and two glasses of water. It fills you up and keeps your digestive system moving.
-White meats such as turkey and chicken are much healthier than beef, pork, and red meat products. Instead of a hamburger meat sauce for pasta, try ground turkey. It tastes the same and is much healthier for you.
-Take smaller portions and go back for more if needed. If you have a smaller portion of food, you're less inclined to keep eating. Larger portions of food inspire you to keep eating to finish. Avoid them as much as you can.
-Instead of three meals a day, try 5 or 6 smaller meals. Try a breakfast of whole grains and protein (granola or (sugar free) oatmeal) or a banana (potassium is excellent) in the morning, a low-calorie granola bar for a mid-morning snack, a high fiber lunch (salad and soup), a low calorie yogurt and granola afternoon snack, and a high protein dinner. All of this can be made cheaply by buying off brands, visiting farmer's markets, and shopping at wholesale stores (such as Sam's Club or Cosco). Avoid Ramen as it has no nutritional value and is really just unrefined fat (as I said earlier, fat is good, but only when it's eaten with protein).
If you want more diet advice or a workout routine, let me know. I went from flab to abs in about 6 months (lost 30 lbs) and now I'm seriously ripped: