There are several preamps in that price range that I either currently own or am very familiar with. For something on the warmer side, the Audio Mirror T-61 is excellent. An older Classe (DR-5) for instance, sits on the other end of the fence; not quite "clinical", but more neutral with a little more detail. A notch toward warmth from the Classe is a Musical Fidelity A3cr, and another notch toward the Audio Mirror is a Marsh p2000t.
All are excellent preamps, and can be had used for about your desired price.
Michael