Have you tried lentils before? They're cheap and they're more filling than rice, but still in that same sort of vein as beans. Unlike dry beans, you don't have to soak lentils before cooking them, though you still can soak them to cut down on cooking time. They're also a little better than beans about picking up flavor from broth or stock, and they don't turn to mush quite as quickly as some kinds of beans will. Throw in a couple of vegetable bouillon cubes and some random produce (carrots, celery, onion, maybe minced garlic), and you've got a meal that will last you several days. Until your roommates get ahold of it, anyway.

Edit: Also, if you're trying to go vegan/vegetarian, pay attention to what kind of bouillon cubes you get. The cheap (e.g. Knorr) ones have animal products in them -- even in the vegetable broth cubes.