My favorite cheap meal is black bean tostada's

I get a big thing of corn tortillas from the store, fry them up in a little oil until they're crisp, put them in an airtight container with some paper towels and they stay good for a long time

Then I just take a big can of black beans, put them in a pot with some seasonings (usually some garlic, cumin and chipotle, but when I'm really tired, I just put generic taco seasoning) and mush it into a fine paste while I heat it up

Then you just assemble it on the tortillas, add whatever fixings you want and eat it

It's cheap, it's filling, it tastes good and you usually end up with plenty of leftovers for the next couple of days