One good knife is probably much better and more usable than a whole
set with the same price. However, very good (japanese) knives require
much more care than ordinary knives. For example they have to be
cleaned and dried immediately after each use. Some of the best
knives may even rust if left lying around.

Many years ago, I thought I'd get a really good kitchen knife and bought a
carbon steel Sabatier (French!) knife. Carbon steel is NOT stainless steel
and it does rust, so you have to dry it after use. Carbon steel has to be
sharpened frequently: I used an Arkansas stone and a Washita stone
from my Scout days. HOWEVER, modern stainless knives are so
good at keeping a sharp edge that I can see no reason for going back to
carbon steel.

Disclaimer: I am not a chef. I use a knife to cut stuff, not for
exquisite preparations with edges to be examined under an
electron microscope. And I bought the Sabatier for non-sushi
kitchen tasks, the usual fish, meat and vegetable fare.