Big jobs - like those with a thousand windows and so on - you'll never get away with pricing up windows at a £1.00 or a £1.50 a pop.
Smaller commercial work is different, but on the larger ones, pricing is massively competitive.
Those responsible for giving these kind of contracts won't think twice about awarding you a job worth...say £80, and you'll knock it out in under 2 hours...great money!
But when you start talking about sums of many hundreds of £££ then they think very carefully about spending their money, cheapest price usually gets the job.
Which also means that relatively speaking the price is very tight indeed.
A glass wall 20 metres by 4 metres, on a repeat clean is going to be knocked out with ease in under an hour.
On work such as this, a square Metre of glass is going to be cleaned in a couple of seconds..ok, 10 seconds, tops!
Depending how dirty the glass is, and the type of seals on the panes, a first time clean might take quite a while to do.
You might get away with £150, and on a first time clean you'll be a good couple of hours on it, but I reckon (depending on where in the country you are) you'd be pushing your luck
If it is a job you know you could knock out in under an hour I'd go in for something around the £80 mark, but that also depends on how swank the company is!!
Ian