Not expensive and i can assure you that you just plug the system like you plug a tv. and calculated that my system can clean your window everyday in couple second for 20 year 365 day per year divised by the cost of 400$ per window the cost come in form of penny for 20 year for a system that secure the job well done and faster and with a frequency that no other can do.It give you the opportunity to have your building tenant having there window clean everyday plus no trouble to do the job risky any more.