Will reiterate what Tammy d 57 posted
the question was about comparing costs
You will get (if you look after your birds properly) a quality product-your local prices
If you have always bought the cheapest eggs and chicken then I would think you would need to seek out local fresh farm eggs and compare them for taste etc.
then you would need to decide if that is far superior to what you buy at the cheapest prices-most of us on here think so but of course that is subjective.
then your eggs are valued at what you want to have your family eating-around here it is 4-6$ per dozen -store prices but of course they can never be as fresh as your own no matter what the store eggs sell at
Secondly -you could find out if you know family or friends who would buy an extra dozen or so a week of your quality product at a reasonable price-more than the cheapest-probably less than the highest
Thirdly-the manure has a cost benefit -either to you or to another gardener
Four-a properly constructed hen house and (or) chicken tractor has a value-you could build for resale if you wished
Five-In addition to grower/layer feed some additional feed can be found by the hens when free ranging-or in movable chicken tractors if moved often-adding extra green feed from the garden or lawn and some quality table scraps (extra brown rice-whole grain bread scraps-leftover egg-fruit peels etc.)
Non producing hens can be processed for the table if you wish
Taking a hard look at what you want for your family and how you can work towards that will give you more of a whole picture
Also if you have children the experience of helping the family produce part of their food is an invaluable addition to their view of their world-
Letting them own-handle and care for a few chickens has way more benefit (IMHO) than getting a hamster or guinea pig (and we have had both)
cheers
grace