Some of the best pre amps used for $600 or less

AES DJH (made by the folks at Cary) is currently available for $699 on Audiogon (No, It's not mine). While I have since "upgraded" to much more expensive preamps the AES DJH is a wonderfully musical tubed linestage at a very good value.

The Doge 8 lists at around $1300. It is a great pre-amp. If you can find it used, gobble it up.

Throw the Quicksilver Audio tubed linestage into the mix, can be had used for about 600. I almost purchased the dared as well, if I saw one come up used for 300 I would definitely jump on it.

I second the Doge 8. Sorry now I sold mine now. Not sure you can get one for under $1000.00 used though.

You might want to look into the Mapletree Audio linestage, two box, tube regulation, variable gain, and $760 new! Made by hand, point-to-point by a retired Canadian electrical engineering professor and audiophile.