You might want to consider a used boxlock from one of the Scottish makers. Makers like Harkom, etc. turned out some lovely stuff with beautiful lines. You could get an excellent piece for under 10K USD and it wouldn't be out of place in any company.
If you're inclined to look at the Scottish makers there's a good article by Gavin Gardiner somewhere on his website.

If you're after a true best gun, you'll probably need to triple the 10K budget for a good used example.