A lot of my favorite ones were 6sn7 preamps. I prefer four 6sn7 preamps, 2 per channel so I can blend 2 different brands sometimes if I need to use as tone control. Ken Rads and RCA’s work well together plus many others or load it with four of the same tube.
I really enjoyed the Don Sachs with the Kootenay. Spratek is very nice. I really liked the Conrad Johnson but ones in the $2000 range may be a little fuzzy and slow great with blues and jazz but can struggle with other complex music. Audible Illusionn or Bruce Moore are nice but can be hard on tubes, I had a VTL 5.5 long ago and really in joyed it. Cary or Dennis Had are very good amps. I had an ugly black box Don Allen preamp that was very special 20 years ago I wish I would have never sold. There are some nice ones out there in your price range.