you have obviously not shopped for groceries anywhere other than NYC.
Prices are usually 50%-200% higher here for groceries in my super market in Queens compared to grocery stores in San Antonio, Texas where I am from. And it is the cheapest one around that I found.
Of course things in general cost twice as much here compared to San Antonio. rent, housing, gas (well about 25 cents more), groceries, labor, driving (tolls vs no tolls), movie tickets, a night out at a reasonably nice restaurant (not even something fancy, just not mcdonalds).
The 2 big ones, labor + real estate costs are going to be a huge factor in the price of food at a super market compared with whatever small discount they might receive from a shorter distance from the port to the store. Not to mention that the US is a net exporter of food last i checked so not much of your food come in a ship from over seas, but a truck instead, though possibly and often from as far away as california.
Please let me know where you are finding a cheap grocery store in this city. Ditto for cheap anything.