What used speaker would you buy with $20,000-$35,000 and why?

If we are going that route we should do LSD or shrooms...

I wouldn't recommend that, based on personal experience. The last time I tried that stuff, an orange rhino walked into my condo from the patio and started berating my modest Ax-7e/P3esr setup, and boasted on how his McIntosh system was SO MUCH BETTER...  :-)

In terms of the thread, if I'm spending my own money I would look at Harbeth 30.2 or Magnepan 3.7i, and bank the rest.

If I'm spending your money, I'd look at either Wilson Max-3 or Tannoy Westminster Royale SE.

FWIW, if it were my money, I would buy a used pair of Sonus Faber or B&W speakers. I'd buy as high in the line (used) as I could for my $20,000.
You won't regret it!

Here’s a pair of the Linkwitz LX521’s with the ASP and multichannel amp - ready to go. I almost bought them... but... already had the Orions and couldn’t justify the expenditure for another set of Linkwitz speakers. Not sure the guy has sold them yet - you might check with him.

They sound like Maggies... but... with better bass and dynamics.  Same soundstage and imaging, because they're open baffle, dipole speakers.  I have the Maggies also... and... I prefer the Orions for the reasons mentioned.  Very much the sound of the live music performance.

https://www.audiogon.com/listings/full-range-linkwitz-lx-521-2015-08-02-speakers-07930-chester-nj

They also sound a lot like the Grado PS-1000e headphones mentioned above - which is spectacular... but... with a more realistic soundstage.

I will sound like a "broken record" with this recommendation, but based
on what I have heard, and considering that you can place these speakers
easily in a medium sized (or larger) room unlike Maggies, the Eggleston
Andra-3's can be had for under $15K with the new carbon-fiber based
midranges.  I had the Andra-2's and they sounded Very Real on acoustic
material.  On well-recorded pop or rock music (such as Steely Dan) they also were spectacular.  They have superb bass below 20Hz also, without
any strain.  Their only competition is a significantly larger speaker system
that can move more air or something else that you prefer the looks of.