Hi Tatman, We use ladders as well but the way we do it is with small vikan brushes and a bucket of soapy water, we add a drop of chloros ( farmers use it for sterlising milk lines, others use it for cleaning driveways etc, its a chlorine based bleach ) dont know what it's called in the U.K
Then rinse from the ground with the customers garden hose, a lot easier than cleaning with cloths. We have started using the backpack for some of the work lately and it is a lot faster. Again we add the detergent etc to the backpack and rinse with the customers hose. Needless to say we use telescopic poles for this with a small vikan swivel brush from gardiners.
As for price, well we are the South of Ireland so its hard to compare but your prices seem very low to us considering the amount of work involved and the dirt etc.