Lately I've been hearing 300-400g each but I'd have to say 400g is a fairly fast sell for these. I have sold these many times at 500g each including today but I would recommend 400g each (To avoid getting laughed at).
As for getting them without doing quests, as far a I know you either have to do a quest or find destroyers on the way to one of the quests. I don't think there is any area that just has them as a drop without having connections to a quest with destroyers in them.