Conrad Johnson PV-5. A Classic. The only reason that you can find one for $500 is because it was very popular during it's production run. At least 3 TAS and one Sterophile reviewer used them as reference preamps during the eighties.
Sleeper preamps: $500 new/used
Looking for tube or solid state pre with very good phono stage...willing to go used and go with an older model if sound quality is superior...any models come to mind?