The value of a knife in my collection is its value to me...not what it brings or might bring on the market. (Where any potential buyer has his or her say on the matter.)
I've owned inexpensive knives and knives that were worth over a couple grand. I've never purchased any of them with the thought of what they'd bring if I chose to move them on.
Some I've sold for less than they were worth (to me), some for about what they were worth, and a few I made some serious bucks on. Many I've simply given away.
If you buy because you want to get back what you put into it, or more...you're better off buying mutual funds and adding to them every time you think of buying another knife with your disposable income.
(In other words, this is a hobby...not a means to financial success.)
No snark intended, but it's a lesson better learned sooner than later.
Here endeth the sermon.