Listen, I know we all love to circle jerk about how dollar stores are evil, but you can walk into just about any regional chain supermarket and replicate the same exercise and get about the same results.
Sorry, real people who are on a real (strict) budget pay attention to the price of goods when they shop. If you are really hurting from a $3 overcharge, chances are you pay very close attention to the register receipt and bring it to the store's attention. Regardless of income, my wife and I routinely scrutinize the register receipt. Force of habit.