The World Food Programme (WFP) data was released to coincide with World Food Day
The United Nations says food is becoming less affordable in countries in conflict or subject to political instability.
The research from the World Food Programme (WFP) was released to coincide with World Food Day on Tuesday.
The UN says in dozens more countries, persistently high food costs are putting the hope of a nutritious meal beyond the reach of millions.
It says around the world, 821 million people go hungry.
WFP's Counting the Beans index covers 52 developing nations.
The aim is to give consumers in wealthy, industrialised countries an idea of the share of daily income needed to secure a basic plate of food in poorer parts of the world.
Taking food costs in New York, USA as a reference point, WFP has found that a resident there might spend US$1.20 (€1.03) to cook a simple soup or stew - such as some beans or lentils, a handful of rice, plus water and oil.
By contrast, a citizen of South Sudan would need to fork out more than two days' income - the equivalent of US$348.36 (€300) - for a similar meal.
While the same would cost a resident of North-east Nigeria US$222.05 (€191); and a Yemeni national would pay US$62.37 (€53).
All three are countries or regions where famine is a looming threat. And in all three, rising food costs closely track the trajectory of conflicts.
David Beasley is executive director of the WFP: "Affordable food and peaceful societies go hand in hand.
"But millions of our brothers and sisters enjoy neither; the presence of near-constant conflict makes it almost impossible to cook the simplest meal."
In many countries, food affordability measured in this way has actually improved since 2017.
In one situation, this could be thanks to strong economic growth; in another, to greater stability, a better rainy season or - in the case of southern Africa - humanitarian assistance helping offset the effects of severe drought.
But the WFP adds that food costs often remain intensely disproportionate in relation to income.
"This is the case across much of Africa, as well as in parts of Asia and, to a lesser degree, of Latin America", it says.
Among the countries surveyed, Peru tops the list with the most affordable plate of food outside rich countries, at just 1.6% of per capita income versus 0.6% in New York.
Laos and Jordan are close runners-up.
"Some of the numbers in this year’s index illustrate the real and personal cost of conflict and hunger," Mr Beasley says.
"They should shock and outrage everyone. We must do everything in our power to reduce conflict and rebuild economies, so markets can thrive and communities can prosper."