Baby chicks cost $6 at a supply store, but I can get a rotisserie for $5? What is the real cost of having chickens?

I do not understand the mathematics behind the dilemma. I'm assuming only the firts chicks cost money, because down the line they will breed.But feeding them, housing them - vitamins and doctoring costs a lot of money.

So anyone with couple or more chickens - how much does it cost to have them on the table? And realistically how many eggs do you get?