Another cost to consider is the capital investment (the durable goods such as cost of coop, feeders, brooder, heat lamp, etc.) The math isn't as simple as cost of chicks plus cost of feed, compared to cost of grocery store birds. By the time you figure in incidental costs, like accessories necessary for butchering, or the question of weather your own time has a dollar value, the accounting is going to come down heavily in favor of buying meat at the store. Like everyone before me has already said, there needs to be some non-economic reason for raising your own: either they taste better, or they are humanely raised, or you know they weren't fed chemical nonsense, or you just simply enjoy the whole process. For me, those are good enough reasons to overcome the price difference.
One final observation: I agree with everything Me & My Peeps said, except for the part about hormones.
Me & My Peeps :
Its done to be sure of the quality of life for the bird, monitor that there are no growth hormones of chemicals in the meat, knowing the history from "cradle to grave" and the pleasure (in my opinion) of raising them.
Growth hormones haven't been legal in poultry for decades. It's a violation of USDA labeling laws to claim your birds or eggs have no added hormones, unless you also provide the disclaimer that hormones can't be used in poultry. I point this out because a lot of people get all excited about hormones in poultry, but it's a myth.
Now, antibiotics, on the other hand, are a different story, and are used widely and routinely in commercial chicken production...