The exact cost of difficult people in the workplace is incalculable. Examining the subject is like trying to watch a skyscraper being built by peering through a knothole in a plywood construction fence. You are only able to see a portion of the complete picture at any given time.
The problem is not only that difficult people make everyone miserable, but also that they diminish your effectiveness and the effectiveness of those around you. Your effectiveness is a measure of how you get things done on time, under budget, with quality workmanship, and without overturning any apple carts, so that you get positive performance reviews, promotions, and raises.