Doesn't the price reflect the version of the driver, and its "used" status? You can get a new Mk IV for around $125 shipped. If the sale driver is a heavily used Mk I (late '90s), does it rate 70-80% of the new price? The general consensus about used electronics/speakers is that used gear goes for between 40-60% of the new price if in good condition. Hopefully the buyer and seller in this case can get what they are looking for.
JP