British chicken breast packet cost about £5.29 per kilo (£2.40 per pound, $2.96 per pound). One of those packets of refrigerated chicken that's "cage free" (another great marketing term) is $9.99 per pound, that translates back to £17.29 per kilo, three and a half times more. The British chicken is also refrigerated,
unlike the USA has regulations on the packing of those cage-free chickens in sheds, and is produced under stringent antibiotic rules. It also has "access to natural sunlight" (marketing term) can be "organic" (marketing term) and is, in reality, produced in largely-similar factory conditions.
What's worrying me now, and it hadn't occurred to me until you posted, is how expensive US chicken evidently is.