The question intrigued me because I work in IT in the financial sector. What you are looking for is a market-data feed. But instead of trying to capture the buy/sell price of stocks, bonds and other investment products, you want the prices of tangible grocery products.
Good luck with that one.
On the one hand, I'm pretty certain department managers at store X are keeping tabs on what store Y and Z are charging for the same products so that they can remain competitive and move their own inventory. But I don't think it is in their best interests to give away their opposition research. Nor do you need them (or anyone else) to do your leg work. You are going to purchase only a finite number of products. You already have a printed list of what you buy and how much you paid. It's your receipt. Stick that in the front of a small notebook. In the notebook, create a page or two for each store where it is already reasonable for you to shop. (Aldi, WholePayCheck, CostMore, SonOfSamsClub, TraderJoe, AsianMarket, and so on) When the weekly circulars show up and stuff your mailbox, compare the price in the circulars for cheese doodles. Whichever one is lowest is where you are going to buy your cheese doodles, so put cheese doodles down on the appropriate store's page, with the target price. Do the same for beef jerky, scooby snacks, sugary cereal with multi-color marshmallows, circus peanuts, etc. No judgement here, eat what you want. Very quickly, you'll have a list for each of your local stores. Keep the notebook in your canvas grocery bag so that whatever store you are in, you have that store's list....because you'll have every store's list. And if you see Little Debbie Snack Cakes at Aldi for even less than what you thought they were going to be at ShopRite, you buy them and note it in your little notebook. And you repeat this for all the things you buy. And thus, you'll have your very own, custom Price-Book.
It is not hard, or time consuming. Some commenters think the price-book is outdated. If a person loves spreadsheets, I don't want to take away their joy. But I find a spreadsheet on a smartphone to be unwieldy when in a store. The little notebook and pen works just fine. And there are new pages, if I need to write something else. I'm in IT, if I thought an electronic version of this would be better for our needs, I'd be all over it. But I don't find that necessary because we buy such a small number of items on a regular basis, that eventually we memorize the price and instantly recognize a good one versus a not-so-good price. It so happens that most of our best price options for foods don't have printed advertisements. These farmers markets and ethnic grocers don't need to advertise or offer gimmicks or sales to get customers in the door. If the big chains are going to beat them on price for a particular sale, they are going to feature the loss leader prominently in advertising. The chain store's hope is that you'll make up for their loss buy overpaying for cheese doodles & scooby snacks and needing something from their prepared foods section. A Price Book is your best insurance against that trap.