cheaper per gram compared to what? If you’re comparing to recent “fake meat” alternatives then that’s probably true. But more traditional plant sources of protein should be significantly cheaper than meat - things like lentils and even soya mince/pieces. Both of these can be bought as dried produce, which not only means they’ll keep pretty much indefinitely in your cupboard but that commercial suppliers can store and transport them without refrigeration helping to reduce costs. Additionally dried produce takes up less space and weight which further reduces storage and transport costs.

Meat comes with unavoidable negative consequences to health. The more meat you eat, the younger you die and the more major diseases you experience. Nobody in the world who is getting enough calories from plants is suffering from a lack of protein. It’s not a real thing.