I would say $50-100 is mid-range, and that sort of money can get a pretty darn good knife in your hands. There are an awful lot of excellent designs and good, but not great materials in that category - frankly, we're spoiled.
$100-200 is approaching the high end for factory stuff, fixed or folding. It better be pretty dang good - better steel and HT, really good F&F, etc. Again, there are several companies providing that sort of thing... and that's great for all of us.
Once you get above the $200 price-point, you're in custom/handmade territory, where for the same money you can have a guy make exactly what you want rather than settling for what the marketing folks at XYZ Corp decided would be a good bet this quarter. You should demand top-shelf designs, steel, HT, F&F etc. You should also demand any option you want, from handle material to blade steel to tiny features like how far apart the jimping is spaced... naturally each extra step or material upgrade costs a bit more.
The list of factories that can provide that level of quality and performance and options is basically nonexistent... you're gonna get what they bloody-well feel like making. If you're lucky, they'll give you a couple choices like micarta vs. G10 or bead-blasted vs. polished vs. powder-coated, and charge handmade prices for it.
The list of handmade guys that can do it is quite long, but their ability to produce big numbers is obviously much less; so you may have to wait a couple months to get your dream knife.
At $400 and up, there is simply no excuse for anything but the very best, custom or factory.
ETA: I have not taken any considerations of rarity or collectability into account here. That's a whole different ball of wax.