I would have no idea, and only you would know what you can charge. Not to sound down on you, but in less you are a very very seasoned vet and have tons of experience in this, you can lose your shirt....as in this is the kind of job that can make you a lot of money or put you out of business. I can't see how tall the building is but unless your willing to flush $10,000 down the drain, I would walk. You'll have at least a weeks worth of paying your guys, at least a weeks worth of lift rental if not 2 weeks, several thousand dollars in chemicals, and if they are not happy, the best that will happen is they won't pay you....the worst that can happen is they sue you for damaging the limestone and you could be forced to replace it all. Not trying to scare you at all, just giving you a heads up so you don't go in blindly. This isn't just a simple housewashing or building washing but more of a restoration project.