I've done it and just bought my own kind of foods and I just stuck to the 5% fat rule. I know what you mean about being expensive but if you think that you won't be buying any rubbish foods or snacks, then I would say that its actually cheaper to eat proper meat and veg etc. You can go for cheaper cuts of meat that need a longer cooking time and braise or casserole them, a slow cooker is ideal for this. Go for the cheaper fish too as some oh Rosemarys suggestions are expensive.