Here's one way to live on $1.70 per day if buying in bulk.

    lentil: 180	g
    rice: 180 g
    banana: 120 g
    olive oil: 20 g
    egg: 112 g
    milk: 99 g
    dry roasted peanuts: 50 g

    cost    : $1.70
    calories: 2000
    carbs   : 200 g
    fats    : 56 g
    protein : 175 g

with macronutirent ratio, calories from = fat:protein:carb = 25%:35%:40%

buying bananas, milk, and eggs in bulk doesn't sound like a great idea given their inherently short shelf life.

Anecdote: Two person household experimenting with meal plans (breakfast+dinner with leftovers for lunch) and our groceries cost about $400/mo. Personally, that number seems very high to me, but it could go down as we prioritize cost over following Recipes As Written. Cost was stable around $300/mo before, but with less varied meals.

Those two numbers translate into $50/person/week and $37.5/person/week.

I wanted to try out Soylent for a breakfast replacement, but was also turned off by the price. Edit: Also the delay! Wow, 4-5 months

Probably by preparing meals at home.

Out of curiosity, how much does it cost to feed a member of your family for a month?