We have 10 (backyard) chickens and spend about $40/mo in feed. We average about five eggs per day when they are laying, so let's say that's 150 eggs per month. That's $0.26/egg or $3.20 a dozen.
But we have to factor in around 4 months of them not laying during the winter. So for laying months, that brings the feed price to around $60/mo or $4.80 a dozen.
So yeah, at current prices, it's worth it for us. I also haven't factored in the value of their compost, which is really quite expensive when you're buying as much as they generate, so it's probably even cheaper than listed.
Out of curiosity why not grow your own feed?
In many cases you can cycle the compost back in to the feed you grow (as fertilizer).
Around here our eggs are averaging about $9 per 12 on the shelves, and you can't buy just 12, the only eggs on the shelf are the 18/24 packs so about $20-22 per pack, almost the same price as choice meat.
FWIW, you can get generally better results with different breeds. Golden Comets or ISA Browns will typically get you 1 per day per chicken. In reality if you had 10 you'd likely get 8 or 9 per day. They also seem to lay in the winter better than many. Unfortunately they just don't live long so it's a constant cycling process.