I read all the time that "dieting is expensive" or "diet foods are so expensive". In my own weight loss experience, I just haven't found that to be the case at all. I think it's all about your approach. I do think certain diet "plans" can be expensive. They are often meant to be. Not that programs are necessarily "bad", but they want you to rely on their products so you will continue to buy them. If you feel like your success is dependent on certain-brand products, you will continue to purchase them.
I think people also use money as a reason that they can't lose weight--they think they can't afford to lose weight.
Portion control and calorie counting is free :) The method I've used to lose 50 lbs. has actually saved my family money. We haven't added anything to our budget for food since I started losing weight last summer. In fact, we've really saved money on things like cokes and processed junk food. I also had a pretty bad dairy addiction, and we buy much less of things like cheese, butter, and sour cream now, which has been replaced by more fruits and veggies.
I find that our main dinner dish stretches a lot further now. I still mostly make the same things that I used to, but I eat a much smaller portion and fill the rest of my plate up with veggies. This leaves us more for lunches the next day.
For help with calorie counting, I use www.livestrong.com , and there are numerous other sites that can help with tracking food.
I spent $140 on two weeks worth of groceries yesterday. My produce tray and fruit bowls are stuffed full of "diet food"....I have a whole watermelon, honeydew melon, several lbs. of apples, oranges, grapefruits, strawberries, avocados, etc. I stocked up on green leaf and romaine lettuce for 77 cents at Kroger, and tomatoes for 39 cents/lb. at Fiesta, for salads. I shop the sale ads to find the best prices on produce and stock up on everything that is on sale.