Gazza
Your profile doesn't say were you are, but around my areas I have known companys pricing jobs at 65p to 70p per window.
Some cleaners will say thats to cheap, because they are used to quoting at £1 per window, but they also worked off ladders, now they have wfp systems but still want to charge the same rate.
This is ok for small to medium size buildings, but when the jobs are bigger their prices need to reflect this.
What I would do is let them study your quote, if they reject it for a cheaper cleaner, ask how much he is charging and then you can decide to ether match it (but offer a superiour service) or beat it.