Our core business is Window Cleaning and if I could give you a few tips:
1) On a large project like this don't charge by the window. Figure out how long it will take you to do the job and base it off what your time is worth.
2) For 3 time a year service WE would probably offer up approx 20% discount off of the 1 time clean rate.
3) Get a signed contract. It is very common in window cleaning for a customer to think they need it 3 or 4 times a year and then decide after the second service that they wont be needing it again this year.
Do you have access to a Water fed pole? This would be great for a job like this. You would clean it nose to glass the first time around then breeze through the next time with your WFP.
Windowcleaningresource.co got a reaction from Thad in Feedback about a large bid