Breakfast will be your cheapest meal, eggs $3/dozen. Yogurt 99c each or get a larger container to save more money. Oatmeal, bananas. Bacon will be pricey, but let's splurge $6. Avocado, toast is relatively cheap.
Lunch, chicken breast, thighs whatever. You can get them for $5-6/lb and even less at Chinatown. That'll go for lunch/dinner. Toss in salad, rice, etc. Canned veggies like chickpeas and beans are just a buck each at Whole Foods. Ground beef is pretty cheap. Veggies like kale, broccoli are a bit more expensive, but again, only a few bucks and you can use it for multiple meals.
Grocery might cost more, but definitely possible to churn out meals at $3 price points. Of course there's the upfront cost of having basic things like salt, pepper, oil, spices, butter, etc.
I live in NYC. Try eating less than $3/meal for a month here. Groceries cost more here. I eat at home for most meals, too.