In really good condition, meaning no buzzing and cabinets looking pristene? $2000-$4000, depending. $1100 would probebly buy you one that needed work done to bring it back to sounding amazing again, like replacing some ribbons.
If there were updates like new Graz ribbons or crossover updates then more, maybe double, depending on what was done and if they were regular Duettas or Signatures.
