This diet is pretty much the standard in many poor parts of the world - rice, beans, and fresh vegetables (in season). Billions of people across the planet have figured out that it's cheap and nutritious. Glad he could figure it out on his own too.
Many people in poor parts of the world get their daily B12 from fecal contamination in the water supply. It's actually an issue because cleaning up the water supply makes them deficient.
I can't find the original article unfortunately, but I can provide a bunch of information that supports that claim:
* Well, meat is no a large (or any) part of the diet of people in many of the poorer parts of the world.
* Animal sources, are the only real sources of vitamin B12 (though yeast is an animal source, so this doesn't necessarily mean 'mammals' or 'fish').
* Feces contains B12[1][2]
* B12 is water soluble.
* In parts of the world where the water is 'untreated,' it is contaminated with feces to some amount. Obviously, the more people and animals that use the water source, the more this is true.
Vitamin B12 is not found in vegetables: it is available,
however, from faecally contaminated water, and this source
is important in the poorest vegetarian societies.
So if you went to such a society and decontaminated their water supply, you would end up with a population suffering from B12 deficiency.
Of all the places to save money, food is the absolute last on my list.