Patek Nautilus is a great starter PP starting at around 20k...
There are some great Panerai's to be had for half that price like the PAM329.
If he was looking for something with sharper lines, definitely the Royal Oaks, RO Chrono, or Hublot Big Bang's Ice Bang, All Black, or Aero.
None of those will hit $40k.... but there are some special edition ones that will come close....
I don't have experience with $40k+ watches but I imagine they're still among this triumvirate:
In all honesty, closing in on $40k are just over-glorified, extra bedazzled, super fine gold and diamonds. Reaching 100k is different.... enter tourbillons