You can get a Burger King Buck Double for, well, a buck. That's over 3 ounces of beef, a piece of cheese, pickle slices, and a bun for $1. Nutrition-wise, that's 410 calories, including 10g of saturated fat, and 740mg of sodium.

On the other hand, beans and rice. I'm not immediately aware of any fast food beans and rice, so let's assume we're cooking at home. A serving of uncooked brown rice is about 3.8 oz, which I can get at my local grocery for $0.27. A serving of beans is about 9 oz, which I can get for $0.36. So that's $0.63. But now I have to cook the rice and heat the beans, which takes money and time. There are actually going to be more calories in this meal: about 550 calories.

So, yeah, you can get beans and rice for less, if you cook it yourself. But not a whole lot less, and it takes time, which is something you don't have a lot of when commuting between your two jobs. And, say what you will about saturated fat, it does make you feel sated.