I found these two posts via megnut.com. Is eating at home cheaper? and Is Eating Out Cheaper Than Eating In? both try to find the more cost effective solution.

In my personal experience, whether living with roommates or alone, cooking at home saves me money AND time. Cooking for myself gave me full control over what I was eating. Whether I wanted something fast and simple for those busy days and nights, or something extra special to indulge in, the price is always cheaper than what I'd get at a restaurant.

It takes me less time to cook something simple than to eat out because it takes a bit of effort choosing where to eat. Walking or riding to and from the destination should also be factored in.

The only consideration is if you buy in bulk, the initial cash out might be a bit higher than a single restaurant meal. However, this pays for itself in the long-run. Like one commenter said, "For $20 you could get approx twenty portions of rice from a restaurant or a 25lb sack of rice which is about 150 portions."

For those who hate to cook however, it's an entirely different case. Not to get into the concept of utility (economics), but that's when one's willingness to pay for basic necessities comes up. That I think should be discussed on another post - perhaps even in an entirely different blog site.