During poverty in Yugoslavia my family and I subsisted on a diet of beans and rice. Complete protein in that combo, enough fiber and calories, we didn't die despite eating that for years.
Where exactly is it a luxury? In India? In Africa?
I'm pretty sure ex-Yugoslavia area has a very good geography, if not better than most countries. You can grow soy there, just like in the USA, you can grow corn, wheat, you can raise chickens, you can do practically anything there, olives, oranges, grapes, forest fruit etc.
What do vegetarians elsewhere eat? Is there a place on Earth where it's cheaper to grow protein by feeding protein to animals, or to just eat the protein directly?
I'm not exactly sure where in the world is rice and beans more expensive than meat? If so, then it's heavily subsidized and is not real free market behavior.
There is a lot to it, but Geography is not a hierarchical system. In this case, it seems Yugoslavia, as with much of Europe, is great for agriculture. Despite the poverty, that is a luxury. Similar subsistence strategies have been used all over the world for thousands of years (only about 12000). There are places where farming is either not feasible, less energy efficient, or where exclusively plant-based diets aren't feasible. Knowledge about how to replace every component of what you'd get from meat being a component of your diet is also a luxury. If its not already a cultural norm to rely on what has been tested to work, then you need knowledge, a luxury many people don't have. Lastly, you need the intent to drop meat from your diet. In your case this was no option and it worked out. Great. Otherwise its more or less a luxury to be able to experiment with your diet. I'm not so well versed as to know exactly where this occurs, but Papa new Guinea comes to mind, and a wealth of curiosity abounds with regard to the geography of the agricultural revolution and evolution of humans which would provide some indicators.
During poverty in Yugoslavia my family and I subsisted on a diet of beans and rice. Complete protein in that combo, enough fiber and calories, we didn't die despite eating that for years.