Depends very much on the breed Little Blue and then demand. You may find some make less than the price of hatching eggs.
We paid £3 for Crested Cream Legbar chicks at 5 days old. They are autosexing so we had all pullets. Good price but poor birds -two died at under a year, one heart attack and one Lymphoid Lucosis. The remaining one is mad!
We paid £5 for Buff Orpingtons at the same age, but they don't reliably sex until 26 weeks in our case -they either start laying or start crowing! So effectively they are £10 per chick if you are aiming just for pullets.
Blue laced Wyandottes only produce 50% blue in a hatch and are unsexed, the remainder is buff and gold. We sell pullets at £30 because of the wastage -75% of the hatch is not what was wanted. Eggs go for £3 each, even in that knowledge, but they are very pretty birds and very strong. So an unsexed chick has to be £8.
So as Hughesey says you need to know what your costs are plus profit and then see if you can actually sell them.
Generally people add £1 per week. But then as they start to sex your stock halves. Top price is at a year old but people generally peak their prices at 16 weeks and call it 'Point of Lay', when they are 10 weeks short or more! I personnally want to buy at a year old, because problems arise at POL.
Visit a large local breeder and see what's what. They are selling at those prices but you will have to be cheaper as you have no established reputation.