Hi @PEF87
What an awesome idea for a gift !
It would depend on what he plans to do with a the sword. A modern blade would definitely be the way to go if he plans on iaito and tameshigiri.
If this is something for artistic and historical appreciation , then you can definitely find something he d love for around $4000 usd.
The condition in that price range will vary depending on the smith and time period. I personally love muromachi blades and decent ones can definitely be had around that range. Id love to provide you with some links to listings.
There are also shinto ( year 1600 + )
And shinshinto ( year 1770 + ) but I am not very familiar with those timelines.
Generally , In my personal opinion, shinto and shinshinto swords will be in better condition but lacks historical and artistic appeal for me.
This is of course grossly simplified description for ease of understanding and you ll soon see that there are endless pathways and considerations to take as a buyer / collector
Happy to help if you have any questions