It's very hard to price jobs up from pictures. Is it outside only? How many 2nd floor windows are there? How many 1st Floor windows? How many ground floor windows? How long do you estimate the job will take you and your mate?
Is it generally easy access? Are there any special requirements when you can and cannot work?
And 6 to 8 weeks is fairly frequent, so the price should reflect that.
And I reckon there'll be other people who'll have been asked to quote for that job as well, so maybe it wouldn't be a good idea for you to mention whatever price it is that you're going to stick in.
nice one tosh its not easy access ,the windows leak, and yes i think a few on here have been asked to quote it
there are some in door windows to clean
i have a price in my mind to clean it 
but it aint cheap 
Leaky windows aren't a problem at all if you do inside too. You clean the outside first, then the inside.
But even if you don't clean the inside of leaky real leaded windows, I still do them, and no-one has complained.
But if it's a regular big job, I wouldn't be toooo expensive; as you know you'll get your time spent on it right down after a few cleans, and it looks like a nice place to work.