I may be wrong, but I think I remember seeing some factory Model 14 boxes that also said "K-38 Masterpiece" on them. I think it was on the earlier Model 14 boxes. I'm guessing that when Smith and Wesson changed over to their model number system, they probably wanted to maintain some continuity for the sake of customer - so the customer wouldn't be confused into thinking this was an entirely different gun. Therefore, if my recollection about the words on the box is correct, one could say that there was a "K-38 Model 14".
As far as the price, that's a hard one. Depends on why you're buying it. I don't buy premium condition vintage guns that are also rare, so I'm out of my territory a bit. If you're buying it to own a near mint uncommon version of gun you've always wanted and will keep forever, that's one thing.
If you think you might unload it in a few years if you don't like the way it shoots, that's quite another. You might have a hard time recouping that cost. Maybe even take a 4 or 5 hundred dollar hit. That could be painful.
On the other hand, the best condition and most desirable collectables (guns, antiques, etc.) usually end up in the hands of those who are willing to pay the most. Anyway, Pythons go for that kind of money all the time.
And speaking of boxes, does this one come with the original box? That tends to add hundreds on a gun like this, and might explain it's high price.