The true cost is your self respect.
IMO nobody needs a franchise. Just get a smart van with a smart system and go out knock on some doors, deliver some flyers and get the business for yourself.
Why in the world would you need to pay someone a franchise fee to do that?
Unlike McDonalds, Subway, or Burger King, there just doesn't exist a window cleaning brand that is recognisable to customers. If there was, then maybe a franchise would be worthwhile, but there isn't. No customer will go "ah its Joe Bloggs Window Cleaning, Ive heard of them, they're good"
Just get out there and do it yourself. Fanchises for window cleaning are a pure waste of money IMO