As pointed out the things to consider is replacements / what you do with the old hens. If you don't want to cull, you either need to retire them but they will still eat and need care and housing, or you need to sell them on while they are young enough to be worth anything. So you might buy your POL in spring and they will be in full lay by mid summer. You keep them until the next summer when they will be just about to moult and then sell them on for £2 each. In the meantime, your next batch are coming into full lay. But you need 2 houses for that period or a bigger single house and leg rings etc.
You should also figure that not many POL chickens are POL. You will usually get a few months of small eggs first and they will still eat during this time. Then at some point they are going to moult and some will probably drop dead, especially with hybrids. You'll get dirty eggs, broken eggs, thin shells and so on. All in, we reckon on 200 decent eggs from something like a Light Sussex laying strain for the first couple years.
At the end of the day the profit is never going to be huge, especially if you factored in labour but that said, you should make a few bob and it will pay for something.