I would agree that pricing at approx 3 times your normal price is roughly correct, I've done a great deal of these cleans over the years, and providing it is no more than window cleaning, and you have full and open access to all the windows, at 3 times normal you should be fine.
If Nathanial can get away with up to 10 times normal price then good for him, but if you are any good it ain't gonna take you anything like 10 times as long to do the job.
Initial cleaning - or rather builders cleans - is an artform for sure, using a scraper and having to knife off just about every pane of glass is a technique you have to develop.
And you should not need to swap scraper blades every couple of windows either, if you are using the likes of the Unger 4" razor scraper you'll be hard pressed to damage glass with even a worn one.
I've recently had a customer accuse me of really badly scratching the glass on some windows where I did little more than 'nib' of some paint speckles.
I actually went up to them, and deliberately tried to scratch the glass with the customer watching, even using the pointed part of a stanley blade scraper and could not mark the glass (I might do a full post on this particular subject, but I'm still waiting to see if events unfold further)
Wilkinson do a cheap 4 inch scraper, DON'T use it as a general tool!!!!!
Works fine when new, but if you were using this particular scraper then I would certainly recommend changing it regularly, the blade on it WILL damage glass.
Georgian windows of course are different, or leaded too come to that, if you ever have to do an initial clean, inside and out on these windows then 10 times normal price would be a minimum!
I like the look of that Porcupine sleeve...not seen one of those before...gonna get myself one I think...
Ian