What Tube Preamplifier Under $1800 to Choose?

Rogue RP-1 is excellent. Responds ro tube rolling so you can tailor the sound the way you want. I really enjoy my time with the RP-1 and never thought of it as a bottleneck 

I would buy that dehavilland III at the price listed all day!  I bought one new from Kara about 5 years ago.  It's dead quiet to a Pass XA.25 and La Scalas, which was a surprise given that tubes can be noisy and La Scalas are not forgiving with their efficiency.  

I've enjoyed my Audible Illusions Modulus 3A paired with SS amp.  You can find used in your price range.

Audible Illusions M3A/B

Modwright SWL-9.0SE "Signature"

Galion P75

+1 @coos that deHavilland is the steal of the Internet. I'd almost buy another one just to have it. The review by Dick Olsher says it all.

About 20 years ago the great J. Gordon Holt pronounced the sound of the Berning TF-10 pre-amplifier so exemplary as to make further advances in the art unnecessary. That judgment has proved to be premature, so wisely I will not go that far. But having lived with some of the elite high-end pre-amplification from the likes of Jadis, Sonic Frontiers, and Air Tight, the deHavilland UltraVerve is currently my first choice in line amplification. At a retail price of $2,495 it upsets the ultra high-end applecart; the point being that simple, minimalist, well-engineered designs can rise to the top while being quite affordable. Low on parts count, but high on tube magic, the UltraVerve scores big in my book.