Best Phono Preamp under $300 ?

The original Musical Surroundings Phonomena sells used for $250-$325. Nothing can touch it among these budget units. I tried a CA 640P and it was a decent little unit, but.... The Phonomena sounds worlds better (clean, quiet, fast as can be) and provides near limitless adjustments of gain and resistance for virtually every cartridge out there. If I were you, I'd stick with the 640P and keep careful watch for a Phonomena. As Johnnyb53 says, that's your best step up, and the price is within your range.