Especially over the last decade, the budget market has really exploded with quality options in the $40-120 range. More companies are using 14C28N, Nitro-V, and 154CM at competitive prices. Both 9Cr18Mov and 10Cr15CoMov are solid with a good heat treatment, such as on the Civivi and Sencut knives. Kizer and Kubey have been especially impressive lately. (Below is my Kubey Hyde in Ultem.) Most run on ceramic bearings now and some of the Kizers are even using multi-row bearings.
There are occasional gems under $40. Petrified Fish has some bangers in D2 at the $30 level. Compromises can become more obvious under $40 and most stuff under $20 is junk. Especially with the way inflation has gone, this end of
the curve of diminishing returns just offers so much improvement for so little more. The difference betwen $20 and $40 knives can be a veritable chasm and $60 opens the quality floodgates. I think I got that Kubey Hyde in 14C28N for around $60.
Higher end stuff is cool but there, the curve of diminishing returns goes the other way. Just conisdering steel, the decent budget steels mentioned above are all pretty good and while super steels might hold their edges longer, it's never by enough that it really matters with a large rotation or occasional sharpening. (All are way better than 8Cr13Mov and lesser steels.) That would matter more if I actually carried the same knife every day but still, you really need a lot of hard use or to be cutting up lots of dirty cardboard to be seriously disappointed by 154CM or even Nitro-V.
Given the increases I mentioned, build quality might not start getting appreciably better until you're spending like $300. For instance, the North Arm Skaha II is easily my best liner lock but at $300, I have lots of sub-$100 knives that get close on action, lock-up, and/or ergonomics. I've had $500+ frame locks and where they really only tend to excel versus a lot of the $200 stuff I have in the heat treatment on the steel. (Again, that can matter depending on your use.) Honestly, most of the $200ish frame locks I have from WE, Kizer, and Kubey actually have better action than the $500+ stuff I've had.
Of course, the overhead in losing or damaging stuff is another factor. (Edited to add, if you want some really nice for your money, get a custom fixed blade on the exchange here. Your money will go a lot longer than with higher-end production folders.)