If there's no traffic it usually ends up being about the same. It's about $15 + passengers for a car (Edmonds/Kingston one of the more expensive ferries). 30 mintes across after you board the boat. Usually you'll have to do some waiting anytime you take a ferry (weekends, lots of waiting).
Unless you have a fuel efficient vehicle, it ends up being about the same in terms of cost. If you're making a trip out here and haven't taken the ferry though, it's a must do.
The route you're going is probably one of the quickest to LaPoosh, although it's a long trip no matter which way you go..
