I made an extra-firm block of tofu from about 50 cents worth of green lentils!
Soak about a cup of dry green lentils in cold water with a dash of baking soda overnight. Rinse and drain well, then add to a blender with 1.5 cups cold water and salt to taste. Blend well, scraping the sides periodically. Pour thin mixture into a saucepan and add 1 cup of water for extra-firm tofu (or more water for different textured tofu), turn on med-high heat and stir until thickened, careful to not let the mixture burn. Turn off heat, add desired seasoning (I used pepper, chili powder, cumin, and garlic), and transfer to a glass container and chill overnight. Gently pat dry with a tea towel before cutting, marinating, and cooking just like any tofu.
You may substitute any dry legume in the method above!