I think it has everything to do with what your expectations of a knife are going to be. If you are simply looking for a cutting tool then a knife over $100 is likely to be too high a price to pay, much less a $200 knife buy.
Knives do "speak" and when one does it can cause you to consider it even at a $400 or higher price. I think we all have a cutoff point on what we are willing/able to spend on a knife. I recently got a couple of customs, a fixed blade for around $250, and a folder for $450. Neither one will do anything my less expensive knives will do, but yet both of these knives spoke to me with their one of a kind styling and lines. I'll likely not be able to get a factory knife with the same lines. Even though the maker will probably make more of the same style knife they are just not going to pop up everywhere you look.
I'm now considering a couple more custom folders, both of which will cost over $500. Are they going to do anymore than my less expensive production knives? Probably not. But I like the uniquness of them, have the ability to pay the price, and they are hollering instead of speaking!
If all I wanted my knife to do is cut I could spend $50 and get one that would probably last me a lifetime and never think about another one, but if I want something that stirs my soul? well then I have to pay the price. As was said earlier; "If you going to play, you have to pay."
So no, a $400 knife is not worth the price to everyone, but to those that it is what does it really matter to anyone else? A lot of definate statements are here declaring that any knife over the $200 limit is not worth the price, yet what about those who think you are nuts to pay $200 for a knife when you could get one for $100, and then those who think a $100 knife is outrageous when you can get one for $50, you see where this is going?
We would all be better off if we didn't worry what so and so was willing to pay for a knife. And I think we are being a bit harsh when we set a price for what WE would not pay over for a knife, and then claiming any knife over that limit is in no way better.
Just a few observations, and opinions for what they are worth.
