Used, I would head straight for a vk-30SE. I would guess you can get one for under 3K. The transparency, dynamics and drive of this preamp win it for me. I've heard it in the same system as my old ARC ref1, and felt it was no contest. There is a transparency and drive to the 6h30 tube that gives it this quality.
Next in line would be the vk-5i.
Next in line would be the vk-5i.