Plant based protein is less expensive and could be also quite diverse. Some of the sources of vegetable protein include: beans, lentils, soy, wheat, barley, nuts and seeds.
The following are some examples of legumes, nuts and seeds with high protein content.
Mature (Large) Beans: The more mature the bean gets, the more protein it carries. Mature roasted soybeans have 39.6 grams of protein per 100 grams serving. They are followed by mature Lupin beans, which provides 15.6 grams of protein per 100 gram serving. Roasted soy beans (Edamame) cost $1.89 per 4-oz. pouches.
Roasted Pumpkin, Squash and Watermelon seeds: Pumpkin and Squash seeds provide 33 grams of protein per 100 gram serving. Watermelon seeds provide a little less than 28 grams of protein per 100 grams of serving. The price for Squash seeds is around $3.99 per 14-oz. bag, and roasted Watermelon seeds are around $4.99 per 1 lb. bag
Lentils and Peanuts: Peanuts provide 23.7 grams of protein per 100 gram serving, and Lentils provide 25.8 grams of protein per 100 gram serving, when consumed raw. Lentils are around $14.95 per 5 lbs. bags and Peanuts are $15.39 for 48/1 oz. bags.
Almonds: Almonds provide 21 grams of protein per 100-gram servings and cost about $7.99 for a 16 oz. bag.
If we assume that a couple consumes a pound of meat combined per meal and has 14 meals per week and then makes the switch to a high protein vegetarian diet, the couple could possibly save $2,200 - $3000 per year.