Does your town or city have a Farmer's Market? Although I am unfamiliar with the availability of farmer's market in the wintertime in cold climates, I do know that, when the weather is nice, the price of produce at these farmer's markets can't be beat. And the produce is fresher than at your grocery stores. Probably less pesticides too.
Also, I have taken to baking bread in my bread maker. I just bought several pounds of whole wheat flour and a few pounds of 9 grain cereal, and that, combined with yeast and a few other staples, will make a lot of loaves of healthy whole-grain bread. The bread maker I found at a thrift store for less than $10 - the best investment I ever made. Works perfectly too.
I found whole chickens, about 4 lbs each, for $2.50 at a local Wal-Mart. They were "Manager's Special," whatever that means. Those chickens went a long way - I shredded one, and had chicken tacos that fed 5 adults, then had enough left over for chicken salad for 4 adults and had enough left over for soup.
Speaking of soup, that is a fabulous thing too. Beans are pretty inexpensive when you buy them dried, and they bulk up a soup very well and provide lots of fiber and protein, and make any soup hearty. Use a base of stewed tomatoes, also cheap, and add in whatever you want. That soup will last a long time. Lentils are an excellent choice too.
Oatmeal is another great low cost choice. I put xylitol on mine to sweeten it, but that might not be available to you. Maybe put a bit of sugar on it, not a lot and add milk. I think that oatmeal is beyond yummy, and you can get those big containers of it for next to nothing.
This web-site also has an amazing thread about slow-cooker ideas. You can probably make yummy slow-cooker meals for next to nothing, and they are very convenient.