Cherry picker 
Budget unlikely to stretch quite so far 
99.999% of windows in new builds are 'easy clean' and can be reached from inside.
health and safety mate you have to use cherry pickers or FIXED ladders on building sites, I did a clean at a site and it was the site manager who told me I had to price a cherry picker into the quote and believe you me it was needed.
problem with builders cleans is that a lot of people are scared of them because they don't know how to price them up ? easy just price 3 times the quote of what it would be without stickers and cement on glass and also the price of cherry picker hire to go on top. if the builder don't like the price fine get someone else.
We mainly do builders cleans.
Ladders still OK as long as you have fully risk assessed, documented and handed to head office and site manager. Tying is obviously best but very impractical. There is no law that states tying must happen.
As stated earlier, most new builds are fine to be cleaned from inside. In the last year I have come accross just two windows that could not be cleaned from inside. The windows on the first clean are undoubtedly best done from inside as you find that you always miss a bit of sticky residue that would be a right royal pain if using ladders, but is a snitch from inside.
Cherry pickers are great but not that practical on site, especially at the rear of properties on modern sites where access for one can be impossible. They also have there own complications in respect of insurance, training, access, maintenance, cost.
One last point; I like your methodology on pricing :