Depending on where you get your chickens (and I'm assuming you are starting with chickens that are about 6 months old or older) you can spend between $10 and $20 per chicken. A modest coop, with inside roofed shelter and a nest box and an outside area that is wired all around and on top will cost about $100 if you buy all new lumber and chicken wire and some hardware for the doors. A water dispenser (3 gal. plastic) is about $15, and a food dispenser, the same. Food is an ongoing expense. A bag of Purina organic chicken food, which includes the grit the chickens need to digest food, is $15 for 50 lbs. We have 12 hens at present, and a bag of food lasts about two weeks, but they also get supplements in the form of kitchen scraps and lawn clippings.
Start-up isn't cheap, but the advantages of having fresh eggs and the "additives" for your compost pile are an added benefit. Also, hens lay well for about three to four years, then taper off in production. We keep our elderly gals because they are basically feathered pets, but you have to factor in the cost/benefit and refresh your flock about every three to four years.
If you decide to keep chickens, get hens from a reputable breeder or a farmer that has a healthy flock. Don't buy from someone by the roadside or at a flea market--they may have diseased birds or "mutt" birds that won't lay well. Do a little reading about the breeds that are docile, good layers, and are adapted to our Texas heat. We have Black Australorps and I admit, I'm a big fan of those large, black, goofy birds that lay gorgeous eggs.