Anthony,
When you first start window cleaning, it's difficult to price any job easily.
Try this method though. When I say 'window', I mean a 'hole in the wall'. If it's a 'hole in the wall' that's a bay window, add £1.00.
BACKGROUND.
Many here charge far more than me, but they've evolved from having no customers to loads and loads of them. So they charge more; since they've nothing to lose.
So if you're just starting off try this.
For every ground floor 'hole in the wall': 75p
For every first floor 'hole in the wall: £1.00
(Doors are included as a ground floor 'hole in the wall'.)
I live in a small two bedroomed house and that would work out as a £7.00 clean which would be a fair and acceptable price for my house.
Regardless of the Working at Height Directive, I would strongly recommend you don't clean above 1st floor using ladders.