It's only on the Chocolate 3, to the best of my knowledge. It's definitely not on the Dare. And no, it won't cost you anything extra if you're on a Premium plan. Really, it can only cost you MB usage, as I don't believe that any third parties have created any paid channels yet. (Hell, I haven't seen a single new channel since it launched.)
For the record, Dashboard replaces Mobile Web as far as shortcuts go. To access Mobile Web, I believe that you HAVE to go through Dashboard, which is somewhat annoying.