The poster in the other thread is correct about beans. Dry beans per weight is definitely one of the better things to buy when really broke. When I was climbing out of homelessness, I was eating rice'n'beans beans'n'rice for pretty much every meal.

I've seen half dozen egg packs for 80c. That could give you some protein. Stir fry it into your rice.

You could also make a very, very, very simple coleslaw with a head of cabbage, lime juice, salt, and carrots.

There's this recipe for flatbread, which is basically flour, salt, and water. Flour may not be particularly nutritious. But. It's cheap!

If you have an amazon account, you could potentially use Mturk to buy some more food. It could be time consuming, though, and would only be useful if you had prime. Just throwing things out there at this point...

You may also try foraging for some extra nutrition. Prickly pears are fruiting where I live. I'm not sure where you're at, but that's one of the few plants I can think of at the moment. Should you be in an area where prickly pears are common, here's a little vid about harvesting and eating the fruit. Flamethrower optional. You can use a lighter. The pads are pretty good, too!

If you have more time than money, /r/foraging may be useful for you. I know it's the middle of winter, but you never know!