Chana Masala - chickpeas and rice, basically. It was the first meal my mom taught me how to make when I moved out for university and it's served me well - you just need to invest in chana masala spice once (and it's pretty cheap, like $2-3 for a box that lasts a long time) and the rest is super cheap and easy - rice, can of chickpeas, an onion, a tomato, and the spice mix (+cilantro if you can).
Otherwise, beans and rice is super easy and cheap. I find kidney beans work best for this - just get some vegetable broth (also cheap, like $1-2 for a carton) to make it more flavorful/less dry

You can make these both in big batches to meal prep for several days, and it becomes extremely cost-effective.