In general, you don't need tons of meat, and by weight, fruits and veggies are going to be cheaper anyway.
But I am a huge fan of lentils. They are cheap: $1 for a 1-pound bag. They are faster to cook than beans, and they are versatile.
Here are some I make fairly frequently:
Lentil spaghetti - Makes a TON. You get a complete protein if you can find brown rice pasta for cheap, but around here it's pretty expensive. So I usually use wheat pasta unless I've been out of town/near a Trader Joe's.
Honey Baked Lentils - Doesn't look too pretty but it tastes quite good. I'd recommend brown instead of white rice.
Lentil Tacos - The toppings can add up, but still cheaper than "regular" tacos. And really tasty. We haven't made meat tacos at home ever since we found this recipe.
Edited to add: I brought this up on another forum and someone suggested wraps with hummus and veggies. Are you keen on hummus? The same person suggested stir-fry (since it's easy with frozen veggies) and adding hummus to the sauce to thicken it up and add protein. Interesting concept I never would have thought to try.
Also, my MIL (Tek's mom
) shared with me a recipe early in our marriage where basically you cook an onion and some garlic in some oil, add some chicken broth and a couple of cans of cannellini beans, salt & pepper and crushed red pepper flakes to taste, simmer, and toss with broken angel hair pasta. She called it "Italian peasant food."
You can sneak pureed cannellini beans into a lot of things. You can put it in guacamole in place of some of the avocado. I put it in mac & cheese for my daughter sometimes.
Also check into different ethnic cuisines since there are a lot of Asian dishes without meat. Or some Mexican dishes with black or pinto beans instead of meat.
Maybe look into a Pinterest account because there's tons of stuff like this on there.