I only have 4 hens, two are currently laying (one has an egg a day, the other an egg every other day). I can sell a dozen eggs for $3 each. I pay about $21 for a 50 lb bag of 20% protein feed. It takes a month and a half to two months to go through the whole bag. I also feed a handful of BOSS (at $5/bag, bought it last month & I still have 1/2 of it). I also have oyster shells, which are about $8/bag, and I bought that over the summer, still 1/2 left. So, grand total would be roughly $14/month. My birds free-range all day, I feed them scraps once in a while. If you wanted to include the intial set-up costs, that'd be about $100 for the coop, $6 for the hens (not counting the 6 rooster chicks I raised & gave away), and about $40 for the feeders & waterers. Oh, I forgot the straw bedding, that was $7/bale, and a bale lasted for 3 months.
So, if the egg-laying is maintained, I can make about $12 a month with two layers, and spend about $16/month during the winter. However, during the summer, I get three eggs a day, the feed cost is cut in half, as is the bedding. So during the summer, I can make about $20/month, with costs being closer to $8/month because of the free-ranging & foraging. During the summer they get a lot more scraps from fresh veggies & fruit, too.