The main reason the used 3W-100 motors cost less is because they weigh one pound more than the DA. In the never ending quest for "lighter, stronger, more powerful, newer", people avoid the old technology even though it works perfectly well. I see a heck of a lot more 3W-100 motors than DA motors flying planes at my club - because they're available, priced right, and they work.

Perhaps some day, I'll buy a used DA - when they are considered obsolete because they weigh one pound more than the BME and don't make as much power...etc....