Have a look at Walmart SavingsCatcher. As you walk out of the store, you snap a QR code on your receipt. They check every other store in your area for the stuff

Have a look at Walmart SavingsCatcher. As you walk out of the store, you snap a QR code on your receipt. They check every other store in your area for the stuff you bought and refund the difference on a gift card if they weren't the cheapest. I've used it a few times with grocery delivery.