Banning would be absolutely impractical until affordable replacements for staples exist. Obviously regional availability differs, but I suspect if you were to go shopping with a vegan or vegetarian in your community they could show you how to eat vegan affordably. You can buy bulk legumes and rice, supplement that with seasonally affordable other vegetables for fiber and nutrients, and season for flavor. You won't be eating a diverse diet, but you certainly can eat cheaper vegetarian or vegan, just by the law of thermodynamics. It way more expensive to feed plants to livestock to then be eaten by you, compared to just feeding you directly. Keep an eye out for seasonal maize family vegetables, squash family vegetables, onions, and cabbage. Its all about when and how much you buy. The only meat that comes close to vegetable pricing per calorie is chicken.