Dragon...
My gut feeling, backed up with absolutely NO hard data <g> is this:
iMac DV SEs have been available for three or four months. iSubs have been available for less than six weeks...
You might have a hard time *finding* second-hand equipment (I'm assuming private sale). If you do, the price will be directly proportionate to the seller's desperation to be rid of the equipment. (If s/he LOVES it and doesn't really want to sell, the price will be close to new; if s/he thinks it's the devil incarnate and is desperate to get rid of it, it'll be a lot less.)
best of luck in your search!