Armor, another place to check might be at your local plow dealer. Around here they usually have a small bulletin board where people put pictures or listings of equipment for sale. Might be worth a try? Happy hunting.
Well, just for reference, later this winter I'm planning on selling my 94' Warren 1.7 yd. mild steel for somewhere in the neighborhood of $900. It has some rust but overall is in very good shape. In your area though that same sander might have twice the hours on it,( as contractors on the coast know we see massive temperature fluctuations and many times customers feel we are "piling on" when we sand and salt). So you may have to look around to find something decent. Just buy what you can afford and be patient when looking. (Don't jump on the first deal you come accross).
Location does play a HUGE roll in used parts availabilty. In the more urban area's you'll find a large selection of used plows and sanders, some almost new, some pretty tired.