With that budget you have access to a huge variety of amps, especially if you’re prepared to consider pre-owned. How about a set of Lamms? It’s true, at 91 dB your speakers are on the edge for 300Bs, but if it’s the SET sound you’re after, 845s might do fine. These MasterSound monos are Parallel Single Ended, but the sound characteristics are very similar to SET, and certainly worth considering if that's the type of sound you're after: https://www.audiogon.com/listings/tube-mastersound-845-monoblock-plus-see-photo-2016-11-30-amplifier...
It would probably help if you indicated the speakers you have; synergy being so important.
It would probably help if you indicated the speakers you have; synergy being so important.