Ellie - your biggest expense would be the henhouse/coop and any fencing/run. If you can pick up anything secondhand give it a good wash with VirconX or similar, the treat with Creosote, inside and outside too, or paint outside. That way you get rid of any nasty bugs that may live in the house, including red mite (that's what the CReosote is for). Better to look for Onduline roof, rather than felt.
We use a homemade run for small numbers of hens, and a small house on wheels (old kiddie buggy), so one person can move it daily. Run is made of blue water pipe nailed onto wooden base square, so looks like a half circle, then attached chickenwire to cover. Very easy to make and light to move about.
As for getting hens, I was astonished when I saw that bog standard hybrid hens now go for about 15 pounds at PoL! We now breed our own replacements. But even with three hens you would get between 15 and 20 eggs per week in spring/summer and probably through their first winter too... so unless you have a number of regular customers you will need to develop lots of eggy recipes....
We sell between 8 and 13 boxes per week @ 1.80 per half dozen, and that covers our costs, including feeding the young replacement stock. I don't think we will ever recoup the costs of the electric netting and the initial costs of the henhouses/garden sheds we use. But I haven't bought an egg in over 4 years from a shop!
