I think often that trying to spend less and live more simply means that you have the best quality and eat better than anyone who spends endlessly at the supermarkets. Mainly this is because no matter how much you spend you will have trouble finding anything that compares to what you can make at home. Most things are made for the mass market so they have added ingredients to account for this; and I have found that this is even if a product is advertised as all natural, no added preservatives, etc. For example, I try to always make my own bread but when I have gotten behind and have to buy a loaf I spend ages in the bread aisle reading ingredients on packets looking for a list that reads only flour, yeast, sugar, salt and water. I know that this is all that is needed to make bread but rarely will I find a loaf with just these ingredients. And, it is never as good as what you can make at home so you are paying a high price (and it will be expensive) for an inferior product.
I know that this mostly comes down to time and that many of us are so busy these days that the thought of making your own bread seems completely out of touch but if there is just one thing that you are going to make yourself rather than buy make it be the snacks for the week. Compile a list of throw together cakes or biscuits (and there are some healthy options in this department) and quickly put them together at the beginning of the week or make up large batches and freeze them. The snacks that you can buy in the supermarket or the ones that you grab with your coffee on the way to or from somewhere are generally not very good and seem to be the most expensive of grocery items. This is a good way to cut some costs.