i knocked on a large house today.... she said she already had a window cleaner but asked for a quote.
So my price was £30 every 4 weeks....... And i thought that was cheap 
So i asked how much her current windy charges.....
£16
obviously a tax evading windy 
He also might be able to do the job in 30 mins. 
45-60mins it would take, one man, thats with cleaning frames & sills aswell.
GOLD, its a house, with windows

big georgean windows, would have to put the ladders into one corner, do the first two "columns" of glass, then move the ladder to the other corner, and do the other two "columns"
ten tops, and i think 8 bottoms.
so about 18 big windows., 4 "columns" and 6 "rows"
anybody wants to do 18 of these windows for £16, has a screw loose.
Even for the bottom windows, a 3m ladder would be needed.