I don't eat chickens but I keep them for eggs so I didn't realise they were this cheap in the shops.
I bought some hatching eggs last year and they were about £6 an egg. Even without that, say I hatched my own eggs which are free (well I sell them for £1/six so I guess call it about 15p). Then you have to hatch it, a farmer would use an incubator which you have to buy and maintain, costs in electricity which has gone up a lot. As the farmer wouldn't have the chicks under a hen they'd need a heat lamp, more electricity.
Then feed - a bag of chicken feed is £17.10 at the minute. That's 20kg. A chicken might eat 150g food daily (less when a baby but people k know who raise meat birds say those breeds just lay around and eat all the time so I guess it evens out?) so my bag is good for 133 days for one bird, or the cost is 13.8p per day.
(So as an aside, I'm selling my eggs at a loss, but I knew that, that's why the shops have put them up more than I did).
Commercial meat birds might be Cornish Cross which reaches maturity in 6-8 weeks, so the feed cost would be £5.80 for feed alone, if the farmer can get the bird to slaughter weight in 6 weeks.
There's so little in there then for clean bedding, vehicle maintenance and fuel, building maintenance, vets, labourers (to provide decent care and husbandry, especially important with the increased requirements around bird flu), profit for supermarket, profit for farmer...
I appreciate the farmer should be able to get the feed a bit cheaper than me but the thing is it's gone up SO much, like human food, lots of farmers are thinking of leaving the industry altogether.