like anything else, worth quite a bit to the right customer, until they become functionally obsolete (f.ex: nobody really cares about Kepler hardware anymore and it's gotten quite cheap)
now, being that mining cards didn't start at $10k per card to begin with, they won't sell at $10k per card on the secondhand market, but they'll do OK.
at a hundred bucks, why wouldn't you pick one up for your folding@home rig, vs paying full freight for a card with a graphics output you'll never use?
