$20k(ish) tube preamps

You won't do better than an Allnic L9000.

https://soundstageultra.com/index.php/features-menu/opinion-menu/106-uncategorized/1031-allnic-audio-l-9000-otl-ocl-preamplifier

No support for the VAC Master? i'm surprised as it's on my short list, tied to my Gryphon Antilleon EVO stereo. Not trying to hijack the thread, but any thoughts on the Master?

I love mine but the Master retails at 28K (possibly more now?), and 40K with phono stage. A used one can come in under 20 but I don't know if that meets OP's criteria. It's definitely a great match for powerful Solid State amps and high power tube amps. Has the classic "romantic" tube sound, while also being extremely articulate and refined. 

I also like my ARC Ref 6 a lot, and the 6SE should be even better. 

There are some really excellent pre-amplifier designs and I have come to the conclusion this piece is often overlooked and can often be a bottleneck in the signal path.  I now believe it is even more important than the amplifier.  Once you narrow down what you desire, hifishark.com is your friend.  

A Supratek or a Don Sachs will compete with $20,000 retail preamps.Except they will cost a lot less because you can buy them direct from the makers and avoid large wholesale and retail mark ups.The Suprateks also come with a lifetime warranty.

I would call McCormack audio, the VRE1 Pre is astonishing.