... I say again. You can eat considerably better and considerably more than just ramen or whatever a 2-3 buck option at a fastfood joint (restaurants will cost you more than cooking will pretty much everywhere.) will offer at less than five bucks a day. I average around $80 a month feeding just myself (and that's with plenty of necessary stuff included -- sweets, chips, occasional soda, whatever), and we're talking pasta (Mac and cheese currently running at ~58 cents a 7.25g box [~8 cent/gram), or ramen if wanted. Bag of pasta's running ~7.5 cent/gram.) rice (3 cent/gram, or about two-three bucks for a two pound bag.), and potatoes (~3 bucks for a big box of instant mashed that'll last for most of a month, and we're not talking small servings.), with cheese and a bit of meat, varying sauces and seasonings, vitamin supplement and a dabbling of junk food.
With the cheese, meat, and etcs. spread out over many meals ($6 bag of chicken, ferex, will tend to last maybe two weeks, sometimes more, so you're looking at something like 40 cent of chicken per day on average. Usually less, honestly.), it comes out to somewhere between one and two bucks per meal, and we're talking a bowl of food that'll put me into a minor stupor if I eat all of it (i.e. three to four servings worth of food per cooking).
Maybe I'm just in a pretty good area for food, I'unno. Having seen other people shop for food, I suspect greatly it's a lot more of people having no goddamn idea how to power shop for comestibles than anything else. Seriously. Price per weight is your golden measure. If they're not nice enough to provide it on the sticker (and sometimes it's a good idea to doublecheck anyway), divide the price by the weight and find out. Find the equilibrium point between cost and quality. I've found it to be pretty bloody low. Saying again: If it's getting over 10-15 cent per ounce or gram (adjust upwards a bit for things like meat and cheese, but you're still looking at <30 cent/weight, usually less than 25), you're probably getting ripped off to some degree. If you're actually smart and you buy in bulk (note, none of this is bulk prices. Those can get even lower, but you're limited in what you can buy that way.). it gets even cheaper by weight. Friend of mine does something like a month worth of pea soup for something like five bucks, iirc, as an example. We're talking a solid sized bowl of soup for ~16 cent a day, and then you can throw in other stuff to improve/expand the experience. Vitamin supplements do help, but a daily runs something like 5 cent a day (last time I got some, it was running ~12 bucks for a 200 or so tablet container [6 cent/pill], but I was getting something a little more expensive for reasons unrelated to price) which is a really negligible increase.
I will give that it can get more expensive in cities, though. Priced a bit last time I was down in Tampa, lot of stuff looked to be a good 50-100% increase in price/weight compared to a equitable store in the area I'm normally in. Which still puts you at something like 3-4 bucks for a very, very solid meal, since the store I managed to ogle was one that normally overcharges on stuff like that.
As for effort. You do have to actually read the price stickers, maybe check out some of the smaller food selling joints in your area, only buy certain things from certain places, and run a little math in your head (or bring a calculator, whatever). But it's really, really not that effort intensive, and a vitamin supplement will cover a lot of potential malnutrition issues (as will just having a more varied diet than I normally eat, which seriously doesn't increase the price by much. Less grains or meat, more vegetables. Not a big thing.). Hell, maybe two or three. Stuff's cheap. But yeah. You get used to shopping like that pretty quickly, and it's not some kind of arcane gustatory obstacle course. Buy as cheap as you can manage to stomach (and a few simple seasonings and additions can extend that list pretty low). That's really all there is to it.