Unfortunately while being vegan is cheaper, fresh greens are still expensive. It's much harder to mass farm most vegetables to the same scale as grains and pulses.
This is the wrong comparison, there's no need to make it about being vegan.
Fresh greens are required for every human every day and every place.
Try to avoid making such tangential comparisons since you're implying, by accident, that a non-vegan diet magically has those nutrients from greens, while a vegan diet is expensive because of leafy greens. Then we end up with ignorant dieters who eat 800 kcal/day and become silly ex-vegans.
A lot of people conflate "going vegan" with "eating vegetables", and that's simply wrong and a bad approach to eating a vegan diet.
My parents were in a Community-Supported Agriculture and they paid roughly 100€ per month for vegetables (100€ / 30.5d ≈ 3.28€/d) for 3 to 4 people year round. Having to process vegetables also changes the nutritionary behaviour to a more healthier way as a side effect too.
It's totally possible, but not accessible to everyone, unfortunately. I think the community garden way is the best way to make vegetables affordable for everyone, in exchange for a bit of labour. Wish more municipalities supported such initiatives.
I mean... if you're on a super tight budget, like $1 a day, you will be getting most of your calories from:
Beans
Wheat
Rice
Potatoes
Oils
Then a couple cents a meal for flavor.
So yeah, on a super tight budget if your only source of food is that $1, probably not. Instead of getting that dinky little can of veggies I would probably go for split peas personally, since they are pretty cheap and calorie dense. But mostly sharing cause I thought they were interesting vegan recipe bases that can be added too. The patties tasted good to me and the pie will be good with more veggies I think!
Hopefully anyone who is on such a low budget will have access to a food pantry or some other resources to assist though.