My tube preamp journey started with a stock PAS3, then a restored PAS3, then a VanAlstine Super PAS3, then a Conrad Johnson PV5, then an AI M3.
I now switch between an ARC SP-10MKII and an AI M3B. Both are sublime, and can be found within your price range. The AI is on the neutral side of tube warmth, the ARC has more warmth, but also better definition.
Biggest changes I noticed in progression was from a restored PAS3 to the Super Pas 3, then when switching from the CJ PV5 to and AI M3 (pre "a" model).
An AI M3 or M3a are true bargains, can be found for about $1k with some patience.