£3- £5 per window, really?
unless your not a real cleaner and do it for dole money and for buying roll ups , then 3-5 a window is mimimum you should charge, and make sure you are not cleaning out of a car especially not a mondeo or you cannot ever post on here again
seriously though
about £1 a unit is good enough for compactish work, or work that isnt a million miles apart, and with ok access ... from there you will soon work out if you wanna charge more or less based on your own personal circumstances and business needs