I started my price book about 20 years ago, and it's not a fast project. It'll take you six months to really get it going -- and during that time, you may not really see the benefits. But once you have it done . . . wow, you'll be able to figure up which store sells peanut butter at the best price (it's Walmart in my area), which store has the best prices on paper products (Target for me), etc.
Then there's the next step, which I think some of you aren't anticipating:
You make yourself a list of which products are consistently cheapest at which stores. So my list might read like this:
Walmart: Peanut butter, dried beans, canned goods, baking goods
Target: Paper products, cleaning products, beef, sodas on sale
Aldis: Milk, eggs, chips
This isn't my whole list, of course. I'm saying that bit from memory.
So, you DON'T shop at four stores in one week. Rather, you decide that this week you're going to Walmart. You're not out of peanut butter yet, but you see that you'll probably need it within a week or two. You have one unopened bag of flour, but you go through it fast. Knowing that you probably won't return to Walmart for another month, you go ahead and buy peanut butter and flour -- but you're buying them at the store you know is your cheapest option. This means you DON'T run out of these things and end up paying more at Harris Teeter, where you'll shop next week. You DO NOT buy paper products at Walmart, even if you're low on them, because you're certain they'll be cheaper at Target, and you'll get there within a week or so.
Similarly, I buy all my spices at a health food store in a nearby city. I don't go there on a regular basis, but IF I'm going for some other reason, I make a list of spices on which I'm running low, and I stop and pick them up while I'm in that area. This means I DON'T run out and find myself paying $5-6 for a tiny bottle at Food Lion.
The only rub in this deal is fresh produce and milk -- things I buy every week. I often run by Aldis and pick up these things because Aldi's is small and easy to shop quickly. Or I'll just pay whatever they're charging for fresh vegetables rather than make a stop at another store.
When I started my price book, I used Amy Daczyn's method, which she outlines in her book The TightWad Gazette. She uses a small notebook with one page for every item you buy on a regular basis -- so one page for catsup, one page for macaroni noodles, etc. On that page, she writes details about prices from each store. So it might read, Food Lion -- 28 oz store brand $$, 32 oz Hunts $$$. If I were starting this project today, I'd probably begin on the computer. I started by sitting down with my receipt after each shopping trip and recording what I'd bought.
This project is worthwhile; it's one of the things that's made the most difference in my spending. Today I know that Food Lion's going to put big bags of frozen chicken on sale BOGOF the first week of every month. I know that canned goods will be at their cheapest in the fall, so I'll buy cartloads.
But, again, it's easy to stop this project in the early stages and say, "I'm not seeing any results." You won't -- for months.