The one in my cab I'm pretty sure I got from ebay, but it was like 7 years ago.  It wasn't used, it was brand new (or a VERY good refurb).  Works great.  Dunno if they're knockoffs or someone just got a bulk deal or what.  I haven't seen them for $6....  The ones like mine (3" ball, supposedly new, USB built in, with mounting plate) I think run about $80 shipped (they'll say $60 or so but they always get ya on shipping).