The Costco near us has a 10' sit/in kayak/seat/paddle set for $300.  We have the older version of it and it's easy to maneuver and tracks well.  The only downside is that it's a little on the heavy side at ~50 lbs.

We usually have DW in the 10', with me and both boys in the tandem (one sitting on the floor in front of me). I was thinking of getting a second one since the boys are getting too big to sit in the middle of our tandem.  We need to use them a bit more before I can justify it, however.