Stack up on: chickpeas, lentils and beans.
With chickpeas you can do hummus, you can roast them and eat as a snack or serve as a side dish with anything.
Lentils are great for a quick creamy soup (you only need a carrot and an onion extra) and it’s super mega tasty. Or you make a lentils hummus and use as a spread. also lentil bread is very good!
These are cheap, high on protein and filling but also very delicious in my opinion.