I cook most of my own food however I often opt for cheaper products over expensive ones (no frills chicken leg quarters average less than 75 cents each) and regularly purchase from No Frills and china town merchents.
I've been able to keep price per meal on average to around $3 per meal based on 3 meals per day (bagels in the morning only cost pennies and most lunches are cheap as well). $300 per month isn't that hard if you ignore whole foods and organic and are willing to cook for yourself instead of buying pre made freezer meals.
We're a family of four (two adults + 1 4-year old and 1 toddler) ... shopping amounts to between 150-230/week. It all depends on a) the bulk shopping and b) the meat shopping. Either of those add to the bill but ultimately save us over time as we buy in quantity and freeze the extra.