It's not quite that bad. First, you can negotiate with these guys and bring them down substantially. Second, if you don't want to negotiate, there are the regular licensed taxi's nearby. It's been about 2 years since I've had to do this so others might have more recent experience, but when you come out of the ferry terminals, you'll have all the taxi touts. Walk out of the parking lot and cross the street, there are normally several of the red taxis nearby.

I find it funny that you can't really see the official taxis when you exit the building (if you face left as soon as you exit the terminal, they're across the street) because they're hidden by bushes. I've always wondered if the taxi touts paid to put the bushes there so you can't see the taxis.