It's very, very easy to eat for cheap with even basic cooking skills. Soups, stews, potato hash, chili etc (as it's coming to winter). Can all be left bubbling in a pan, then be frozen in portions for later.
Simple things such as getting a whole roast chicken, using the breasts, legs for a full meal, stripping all the meat off it to add into stew, risotto, whatever. Then using the bones to make a stock. Mince is also a really cheap meat to get and can be used to make loads of things.
At a push when I was a skint student I got food down to about £2 a day for three decent meals, so that's about $3.15/day. It was no frills, but did the job.
Two things are key to this, find a damn good butcher, you'll have to look around but you'll find better value meat (not necessarily cheaper, but better quality for same price). A fresh green grocers, veg tends to be a little bit more expensive from a grocers rather than a supermarket but the quality tends to be higher. And never buy organic, it's just a bloody rip off.
EDIT: I suppose it also depends on what portion size you have, if you eat like a horse then you'll end up spending more.
