There's a great analysis on chickens in Good Eater:
If you haven’t noticed, there’s a nation-wide underground craze for backyard and urban chickens, to which I too have fallen prey. Yet the farmer in me has not yet smothered the MBA. The following is an objective analysis of whether or not the output of backyard chickens can ultimately “re-coop” the costs. The answer was surprising, and I have produced 5 key recommendations for economically raising backyard chickens.
Friends frequently ask me whether or not raising my hens is “cost-effective”. Everything I’ve read on the subject in blogs and books says NO. Instead, enthusiasts emphasize personal satisfaction and pet-potential. These are no doubt the true goals of backyard chicken-raising. Yet I am weary of deflecting this common question, and I am happy to further study my birds. Not to mention that my personal flock serves as a wonderful test case. I raise two hens (the minimum flock size) in New York City (the most costly and crowded environment). If I can do this cost-effectively, anyone can!