The short answer is between $250 to $500.
So much depends on the steel type, the handle material, fit & finish and of course labour.
The five knives that I showed in this thread average $132 in material costs alone, with a low of $114 and a high of $175. With the exception of #5, they average 12 hours of labour. I had 28 hours into #5. These material costs and hours do not include the sheath, which is another 4 to 8 hours depending on tooling and complexity. So at $10/hr the cost easily gets to $250, at $20/hr we're at $375 for the knife alone.
Material costs have risen substantially over the last couple of years and I am getting close to the end of my stainless bar stock supply.
What used to cost about $22 / foot is now running $45 to $50. Fortunately I have a decent supply of handle materials,
and shouldn't have to buy much, if any before I quit or die.
What a lot of people don't realize or take into account when looking at the cost of a custom knife is the equipment and supplies used.
Some makers choose to use very basic equipment and go the angle grinder and file route to profile and bevel the blade, harden by torch, although not advised for a stainless steel, then temper in their kitchen oven.
On the other end of the spectrum, there are makers who have all the latest and greatest in shop equipment, multiple 2 x 72 grinders, multiple bench mount disc grinders, multiple heat treat ovens, lathes, cryogenic systems, etc. But, in the end, the outcome can very much be the same quality, depending on the makers skill level.
Myself, I sit somewhere in the middle with shop toys, but having started with a 1x30 sander I definitely wouldn't be without my 2 x 72 grinder, 10" disc grinder and the heat treat kiln. This is a hobby for me, so I tend not to amortize the equipment cost into the cost of the knife where others who make knives for a living may have to.
Pardon the long post.