$725.
 
The ad declares the unit to be circa 1979
 
http://losangeles.craigslist.org/wst/msg/1064867439.html

I think recent prices have been in the neighborhood of $550 or so.  Personally I think these older ones with the red caps and no name on the front look cool; but I don't think there is any appreciable difference in sound from newer models.  So my guess is that $725 is on the high side.