i did 5 for a landlord in Catterick, + windows cleaned on properties = £290 , £50 per house front and back, i got fed up charging lower prices, all ladder work, you risk your life charge on that view, why do you think they dont do it, they can always borrow ladders dont undersell your products. even with a vac, youve spent on good equipment, you never see an electrician or plummer saying ,,, eeeerrrrrr give me a tenner. you have to do lower pricing on windows to keep custom, but other demanding jobs, be proffesional, maybe let them get a bit of discount to keep them sweet, recomendations matter.