Would you pay $0.98 per pound for potatoes if you knew you could get them for $0.35 per pound elsewhere? Would you pay $1.99 for pork chops if you knew they went on sale regularly for $0.99? How do you know when a sale is really a good sale?
As far as I can see, there is only one way to get the lowest prices on food. It is commonly referred to as a price book, but I find a chart easier to work with and fit in my purse. First, list all of the most common ingredients you buy. Here is my list, basically divided by where they are in the store:
white wheat flour
frozen green beans
Your list will probably look different.
Next, what stores are in your area? The best way to find this out is the yellow pages. There were stores in my town I didn't know about. Most of them were high priced Mom-n-Pop type stores, but I found a small market where I get most of my produce for way less than anywhere else.
I also live a short distance from the biggest city in Maine. I go there frequently, so I included a few stores, but certainly not all. I included a Dollar Tree with a big frozen section and a Save-A-Lot, which we don't have in our town.
So I have Walmart, two in-town supermarkets, the local market with good produce, Save-A-Lot and the Dollar Tree. If you have a Sam's or BJ's membership, include these. I went into all of them and got their regular price on the items on my list. This is a time investment, but it will pay for itself quickly.
Walmart and Save-A-Lot have the most general low prices. Walmart has a better selection, but Save-A-Lot has better meat prices. One supermarket has the best prices on cheese, dairy and ham. The other supermarket has high prices but good sales, along with an "almost expired" produce rack, where I can add variety to my produce menu I would otherwise not afford. The local market has the best price on produce and a few other things. The Dollar Tree has the best price on strawberries ($1/lb, frozen!) and a few other things.
Now, with this knowledge, I DO NOT GO TO EVERY STORE EVERY WEEK. I go to Walmart every week, because that's where I get my flour, eggs, and butter, which I seem to run out of a lot. When I go to the other stores, I go to buy several weeks worth of what they have cheapest.
I check www.mygrocerydeals.com almost every week to see if any of the stores are having worthwhile sales on my ingredients. This website is an excellent free resource that gathers the sales flyers for the supermarkets in your area.
I also have a basic price guide for buying things that aren't in my regular menu when the mood strikes. I don't pay more that $1.50 per pound for meat or more than $1.00 per pound for produce, with occasional exceptions.