First tube preamp recommendations (under $5k)

+1 Modwright LS100.  You can pick up one with optional tube phono stage for 1/2 your budget.  I run a McIntosh C500T in my main rig and I am shocked at how well the Modwright 100 performs in my second rig.

I went through this exercise.  Considered all options with budget being secondary. 

Ended up going Prima Luna Evo 400 integrated and got it well under 5k.
I have nothing but good things to say about this.  I have relatively inefficient speakers (Dynaudio Evoke 50) and it drives the hell out of them.  The website is worth a read.

Recognizing this might not be an amp I pass down to my children, for my ears and money, this gives me great pleasure.

cary SLP98p in your price range even with mods.   Have had mine for years and it still warms in the most pleasing manner.  I'm run mine with a variety of SS mono-blocks and couldn't be happier.  Also I am currently using a superb Cary 200ts DAC as a digital preamp in my office.   It has selectable tube  and SS stages for the analog outputs and again hooked directly to monoblock SS amps, crazy nice and the 200ts is currently on sale from Cary for $1900.

How about a restored AR SP-3? Steve Guttenberg seems to like his...: https://www.youtube.com/watch?v=ImDH4k5LrlM

There is one on eBay right now: https://www.ebay.com/itm/294197206930?mkevt=1&mkcid=1&mkrid=711-53200-19255-0&campid=533...

New:   Audible Illusions M3B.   Best value for the money and meets your budget.

Used:   Upper end CJ or Audio Research Ref Series, or SP-10II / SP-11

Vintage:  Mac or Marantz

Benefit to used or vintage is the ability to resell for your cost (or maybe a little more).  Easy to try then decide if you like it.  If not- you can move on to another preamp.

My experience:  I own a ARC SP-10mkII and AI M3B.  BOTH sound GREAT, with with different virtues.

M3B   DEAD quiet- I can not hear it when it is on.  Soundstage is wide, deep and detailed.  MM Phono stage is excellent.   Very natural sound.  Dual stepped volume controls sometimes makes exact channel matching difficult.  But over time you find the (personal) gain setting that works best.

SP-10mkii   Slight noise floor.  Excellent phono stage with multiple loading choices.  Soundstage is wide, deep and detailed.  Overall sound is slightly lush and more tube like than the M3B.  May not be as accurate, but I like it just the same, and in some areas it sounds better.

Macro view is your expectations and budget are realistic so that you can explore the sweet spot of the market.