The TLDR version: They start at $100 for a small knife.
Materials, design, finish, embellishments, and any accessories contribute to the price. 440C is cheaper than CPMS35VN (considerably). Brass bolsters are cheaper than Stainless ones. Micarta is cheaper than Stabilized wood. Wide or thick stock costs more to purchase and takes more work to shape and finish.
Speaking of finish, it’s cheaper to go with a satin or brushed finish than a mirror polished finish. Note: Steels with Vanadium can not be mirror finished, like CPMS35VN.
Filework adds a significant amount of time, as does engraving.
A simple Kydex sheath is cheaper than one with an aluminum frame that you can mount all sorts of things on (like fire starters, sharpening stones, paracord etc.), and cheaper still than a tooled, tattooed leather one with exotic inlays.
Displays and knife blocks vary greatly in cost as well.
Example: A chef knife made with 440C, hollow ground, with a satin finish, no bolsters, with a micarta handle is $300. The same knife made with CPMS35VN is $475.