Thats too scientific for me!
We just look at the house and decide on a price
We dont as such have a pricing structure
In fact we have neighbours with the same types of house at slightly different rates a few quid more/less.
Its more about time for us, if its a big property we work to 2 men £50- £60 per hour as a rough guide.
As said above i think if i counted windows on a quote and charged a £1 for each one pretty much every house we do would need to double in price!
You know where the area threshold is, this has more bearing than a cost per window i feel