All I can say is, regardless of what NADA says its worth - What is it worth to you?
Obviously, if you can buy the same thing (or something very similar) for thousands cheaper, why would you pay more? If it's a one of a kind, then it's up to you to determine what your willing to pay for it.
That's the hard part about buying any RV (new or used). You have to do your homework and comparison shop to find out: "What is it worth to me"? If it ain't worth it, you move on. When my gut tells me no, I listen; I look at as my higher power sending me a message.