I also draw a distinction between Cost and Useability. I do not think expense should define 'useability'.
I collect small to medium fixed blade knives and have more than I could ever use. On the other hand, I have purchased some 'expensive' folding knives specifically to carry and use. My daily carry is either (or both) a PJ Tomes single blade lockback in 420V with pearl scales, or a Tomes two-bladed double lockback with 52100 blades and stag scales. They were each +/- $600.
I think this 'price' estimate for using will vary from person to person, depending on their relative amount of 'spendable' cash. But I think it is a mistake to think that beyond a certain price a knife can not be used.
I still hang on to the idea that a knife should be used, and don't own any knives that I would be completely unwilling to carry and use. But there are some that will probably never get used, or sold. Some of my knives are more art, or examples of extraordinary hand craftsmanship than useable tools. Some of those knives were not terribly expensive.
I carried a gerber LST for years while I bought a number of fixed blades costing several hundred dollars each. Shamed by my brother by admitting this, I purchased, carried, and used production pieces in the $100 to $150 range. But now all I am really interested in buying, carrying, and using are custom knives.
I know a couple of collectors of Expensive knives who admit to never actually carrying anything but inexpensive production knives. I can not understand that. Carrying and using a high quality knife should provide happiness that is well worth the cost and potential risk. Once the money is gone, I have the knife. And whether I use it or not has less to do with its cost, and more to do with why I bought the knife in the first place.
Para