Price and what you find to be valuable might not be related. For example, I have a Spyderco manbug in H1. Its not a horribly expensive knife, but its pricier than a lot of people might suspect, due to the steel. But for me getting a small knife in H1 was well worth what I paid for. There may be a certain designer, or style that you like, and so you might be willing to pay more for it. I might not find the same value because I'm not you.
Materials can add costs, as can fit and finish, do you want a perfect knife, or are you happy with one that looks a little rougher, but has a better steel?
I think biggest range of quality is going to be found in the first 100 USD, about half as much difference between 101-200, and so on. Of course those are subjective measures, and they are also looking at very wide averages. There are a lot of knives that both punch far above their weight class, and some really expensive knives that one struggles to understand why the price is so high. Once you get into international shipping and other currencies, those figures all shift again, as a function of deciding if the additional cost and headache makes a knife no longer desirable.
Most of the knives that I've owned and really like, and fit my style are small fixed blades, under 4 inch, and medium/small folders. For the most part the value sweetspot for me sits around 120-140USD, past that a knife has to really show something special, and below that, its probably not going to do what I want. That said, I do own several SAKs and carry them often.
As for the other topic, every lock will fail, and every knife can be broken.