Personally, I just keep a spreadsheet and put in whatever money I spend on the birds (and the date, helps to keep track of how much feed they go through) and how much comes in, including gas money if I'm taking a load down to the auction, but I can't accurately calculate electricity, so I just try to use energy efficient equipment where I can. I use brewer's grain to help supplement feed, plus free-range. During the summer, I have almost no feed costs, as the free-range and brewer's grain covers it, though I do get a bag of feed once in awhile (spreadsheet isn't on this computer). When I started, I also bought dozens of eggs at the auction. I'd spend $0.25/dozen eggs on most (ameraucanas and pekin ducks were more, $1.75/doz and $2.25/doz respectively) and then sell chicks at about a buck a piece or take them to auction, where they typically sell at $0.85/each. It's a risk that you get bad eggs, but for the most part, people were honest and you'd get good hatch rates (I got 8 pekin ducks out of a dozen eggs, for $2.25, then electricity). I then sold a young pullet and a drake for $20 out of that batch, shortly after I could sex them. I'll have to keep going for awhile before I see the true outcome, since this is my first year using my own breeder birds to hatch/sell eggs, so I'll have to break down winter feed costs to see if I make money in the spring. But, in general, I try to be very thrifty with feeding and maintaining my flock, which reduces costs IMMENSELY.
Another thing with POL pullets, especially in heavier breeds, is you get the males "for free". Charge enough to cover rearing for the pullets only, then add a little for profit, then you butcher out the males and they're "free" by way of having their costs covered by the pullets. Pullets here go for about $10 for unknown/older aged birds or up to $20 for a pullet of a rarer breed (silkies are huge here). Silkies cost even less to feed, lol.
Another thing with POL pullets, especially in heavier breeds, is you get the males "for free". Charge enough to cover rearing for the pullets only, then add a little for profit, then you butcher out the males and they're "free" by way of having their costs covered by the pullets. Pullets here go for about $10 for unknown/older aged birds or up to $20 for a pullet of a rarer breed (silkies are huge here). Silkies cost even less to feed, lol.