Go to HyVee, Dahls, Fareway, Wal-Mart and buy all of these products(same brand) at once and I bet there isn't a 5% difference. I could be wrong but 15 years ago there was less than a 5% difference between Hy-Vee, Dahls, Fareway, and some other east side grocery store that I forget the name when we shopped for these items. This wasn't a public test it was just to see how our store compared to competitors. With that said, there is even price difference between Hy-Vee's but not that much.
This isn't the list but it was something like this but 8x as big
Milk
Eggs
Bread
Pasta
90% Ground Beef
Canned Beans(Chili,Light and dark Kidney)
Canned tomatoes
Oatmeal(Oats and Instant)
Apples
Bananas
Tomatoes
Potatoes
Celery
Carrots
Canned Veggies(Green Beans,Carrots,Corn)
Broccoli
Rice
Onions
Yogurt
Taco Shells
Shredded Cheese
Butter