You live on 50$ a month? Wow crazy in the us that would buy you rice and beans that's it. Chicken here is super cheap, I paid 1.39 a lb the other day. For comparison red potatos are 99c carrots are also right around 1-2$. There really aren't any fresh vegetables except russet potatoes and onions that cost less per lb than chicken. There may be a million varieties of vegies out there but the grocery stores don't stock all that's many, the poorer areas are especially bad. My grocery store is well stocked I can even get more exotic things like radicchio endives and artichoke but in the store near the low income housing... nada. Carrot onion lettuce broccoli and maybe one or 2 other things a lot of it looks pretty wilted plenty of chicken and pork thought.

Anyway optimizing food for calories/impact is kind of a foolish errand unless you are trying to survive in outer space. Food is so much more than calories and nutrients, it's social, its pleasureable its cultural. Telling people to stop eating meat to save the environment is like telling them to stop making art and going to church because it's wasteful and serves no purpose.