What is a very nice sounding tube preamp?

Joule Electra LA 100 Mk III is a good one, and you should be able to find one at a fair price. Read the reviews from when it came out. I have one, and like it very much.

I own a Vac Standard and have to say it is a very good preamp.
I have tens of thousands of equipment. And the VAC Standard is a match.
I have mine AC from a Furman REF20i via a Pangea AC9SE powercord.
I paid $1,400 for mine here. With the upgrade that one has YES grab it.
The VAC Standard has a separate power supply, and is RCA in out only. four tubes two 12Au7 and two 12AX7. Runs very cool. I leave mine on 24/7 thhree years now.
It really IS a $4,000 preamp.
That is only the second one I have seen. I bought the first. So they are rare enough not to pass up.

In addition to the previous recommendations, all very sound,

I own a new , Jolida Fusion, owned a Audible Illusion 3a bought used. Both at your price point and very good. You might also consider Quicksilver.

Enjoy and let us know your choice.

The Joule Electra LA-150 SE and the LA-300 ME are both excellent. I recommend trying to get a used LA-150 SE, get new tubes and you'll be in audio nirvana.

Quicksilver real nice!