Can you get your trailer inside the space? Water supply? With a 21" reclaim surface cleaner pulling around feed hose and reclaim hose going to take you frigging forever. The reclaim surface cleaners are slow because of the suction. Got to look at opportunity costs. You’ll be on that job for a month.
And 26’ high walls around 260k feet is a ton. Why would you give that away? You’re looking at a building that is roughly 430 by 600 ft. - so that’s roughly 2050 perimeter * 26 so that’s 53,000 sq ft of wall you’re doing for free. That’s the equivalent wall space of 15 -2400 sq.ft houses. Never done that much interior walls but around here going rate is about .06 - .07 per sq ft of building for exterior walls on industrial.