A nice preamp in your price range is the Cary SLP50A. I use one I purchased on Audiogon with the Jenson copper/oil caps and remote. Add RCA 6CG7 tubes. Very nice IMHO. Under $700.00. The Agon member I purchased the preamp said it was as good as the Cary SLP98 he purchased. That would be a matter of opinion.
Good luck!
Good luck!