To answer your question of quality construction, every Newmar is built using the same construction methods on the same line in the same factory by the same people. The crew who builds the Bay Star gasser also builds the King Aire. Not every company can say that.
What you are buying for the extra $$$ is extra stuff - very, very nice stuff though. :B (nicer cabinets, higher HP, etc)
Of the 4 choices you're looking at, a Mountain Aire would represent the best value, the King Aire will offer the highest level of luxury. And thats saying the Mountain Aire doesn't offer a lot of luxury itself.
For pure function and quality, any of the 4 you're asking about will certainly get the job done. How much extra you're looking for is a decision only you can make.
On a side note, we're on our 3rd Newmar, if we ever buy another it too will be a Newmar. They have served us very well and Comfort Drive is a game changer. If everyone knew how good Comfort Drive was no one would own a coach without it.
