It also depends what service you offer as well, I know window cleaners who just blade and do not detail so they fly around their work. So as a customer they would begrudge paying a high price for that service as they see the time that is spent.
Then there are ones that detail, wipe the sills and sometimes the frames. This takes time do that so charging a low rate would not be business like.
The thing is we have to ask why will people not pay that amount of money, I find they will if you sell yourself as a business you will get those prices in any area. They will pay for that if they know you are a reputable person and conduct yourself in the right way.
Try this method the next time you are asked to quote, for example 3 bed house you normally charge £4. Say to them you have a min price of £7.00 because you are a business and you spend £300 + on insurance, licenses etc.. before you even start. If they reply back that is way too expensive , just be polite and walk away. 8/10 I have experienced that they call you back as you walk down the path.
You will soon find that as long as you offer a good service they will stick with you and then in the long run you will have all these new customers which are good earners. Then you will soon realise that there is good money to be made out there.
There is a big fear factor that you cannot charge prices like that because you will be undercut by joe bloggs, fine , but why would you want to clean someones windows that does not recognise what a good service you provide. I wouldn't, I prefer customers that respect you as an individual and the good job you do, I pick my customers now, not them picking me.
Give it a go as others have done this and now are beginning to realise what is the point of working your pants of for so little money when you can earn the same at high prices and take life easier.