>It doesn't look like there _are_ any Walmarts in NYC? Are supermarkets in NYC actually offering the same prices as supermarkets in places where there are Walmarts?

That's true. There are a couple of Costcos, but since I don't own a car (like most New Yorkers) it's not all that useful.

And supermarkets in NYC (in car-centric places some NYC supermarkets are smaller than gas station convenience stores) are definitely more expensive than supermarkets outside NYC.

What's more, the "food deserts" that Mamdani's proposal is trying to address don't have any supermarkets and folks are forced to take the bus or the subway to shop for groceries. I'd also note that most subway stations do not have elevators, making it much more difficult to shop for any length of time, especially for older, less mobile folks.