That is £17 with free P&P. Reasonable value if you don't live near a feed shop, but I'd normally pay less than half that price.

So far we have had three chickens for two weeks and are not halfway down a 20kg bag.

So, say you've used up 9kg (which makes the arithmetic slightly easier), that's 3kg per chicken for two weeks, or 1.5 kg per chicken per week.

At that price, they've cost you £1.28 per chicken per week.

Purely out of interest, how many eggs do you get from a chicken in a week? I appreciate that this isn't just about eggs, but I'm curious to know what the cost per egg is.