The SP14 is, IMO, one of the great buys in audio. Rich and linear like the Cary SLP-98 but *much* more transparent and responsive, with a quieter background. Compared to the SP14 I find the Cary a bit thick and slow, but still very musical. The Don Sachs versions are nice upgrades and can be found used (he no longer makes them) but the newer SP14s are no slouches. They’re based on John Broskie’s "Aikido" noise cancellation circuit, next to the Williamson amplifier one of the great contributions to public domain audio circuits.
I would also look at the LTA Velo, which is a preamp/headphone amp but just about in your budget range. David Berning is a brilliant designer.
I haven't heard the DeHavilland but I have very good memories of their 76-based preamp, which was super-musical.