NRG Control Amp A150S - Ballpark value?

Helping to simplify a household that's moving after the death of the techie -- can't find where to start with the sale of his NRG Control Amp Model A150S. Saw some discussion of it here. Can anyone give me a reasonable starting price? It works great, but the family is moving to a much smaller place and doesn't need so much high end a/v equipment. I can't seem to find a ballpark price anywhere.