all you need to figure out is how much you need to be charging to make a good living, you might not have a huge mortgage like other window cleaners in your area so you could be cheaper, however you might want a ferrari lifestyle so price accordingly. stop worrying what everyone else is charging. you'll soon realise if your charging too much ot too little.
if your enough of a bitch, just invite all the local window cleaners round to your gaff to give you a price,that should give you a rough idea.