This assumes that the cost of a chicken reflects the value of the chicken's life. Since the chicken has no influence to speak of over that cost, this in turn assumes that humans (collectively, making up The Market) have a good estimate of the value of the chicken's life.

But (1) it seems fairly clear that The Market doesn't give a damn about the aspect of the chicken's life we're concerned with here, and therefore there's no way for the price to reflect that value (as opposed to the value of the chicken's dead body to us, which it certainly will reflect), and relatedly (2) we already know what humans collectively think about the value of a chicken's life (namely, that it's extremely small). Anyone who's asking this question at all is already doubting the common wisdom about the value of chicken lives, and would therefore be ill advised to take The Market's word for it.

(#1 is perhaps an oversimplification. It's possible in principle for people who assign some moral value to chickens' lives to influence the price; e.g., if they buy chickens in order to set them free. But this will only have non-negligible impact on typical chicken prices if those people buy an enormous number of chickens, which requires them to be very numerous or very rich or both. Especially as a serious attempt to improve chicken welfare this way would be a lot more complicated than just buying chickens and letting them go; I doubt chickens do all that well in the wild. You'd have to provide them with somewhere to live. Actually, most likely the biggest effect of this on the welfare of chickens would probably be via whatever the change in price did to the already-existing chicken farming industry. Higher prices would presumably mean fewer chickens sold but more profit per chicken, which probably would end up improving the lives of farmed chickens and reducing their number. But, again, not going to happen until such time as there are a lot more people very keen to improve chickens' lives.)