Like any other economic decision we make - what's your next best alternative? This determines your negotiating position. If you can find what you want for less money somewhere else, then by all means move on. What is this coach worth to YOU?
I would never let a number in the NADA book stand in the way of a coach I really wanted. This isn't like buying a used car - much fewer transactions and vehicles are hardly ever identical. Only reason to worry much about NADA is for the financing - and if it's that close for you, this may not be such a good move for you anyway.
