The 25-cent deposit on a shopping cart (that's the amount here in Minnesota) isn't just a way to prevent theft of shopping carts. It also saves Aldi from having to send out employees to gather up shopping carts from the parking lot. Another way they save money is by not giving away shopping bags. They charge 15 cents for a rather sturdy reusable plastic shopping bag. Of course, that's optional; you can bring your own bag(s). (I understand that's a common practice in the UK, but Aldi is the only store that does it, that I know of, in the US.) But the main way they keep costs low is by offering only one brand of everything, often the store brand. This enables them to make the whole store much more compact. All the produce is prepackaged; you don't get a chance to sort through a huge pile of apples and select only the best-looking ones. You bring home your bag of apples and find that some of them are misshapen and ugly, but still wholesome. Consequently, there is less waste.

I'd probably go to Aldi more often, but their stores aren't very conveniently located for me. The do tend to be in poorer neighborhoods. See Aldi at Wikipedia.