I have one of the seat mounted yokes that Solus linked to - the one for the fixed bench seat - bought it in 2005 for my RX Rendezvous - think it was @ $120 then, including shipping (bought from Wenonah) - $169 now - yikes!

I don't really like it - just does not seem comfortable to me - seems like the width of my shoulders is too narrow to allow enough room for my head to fit easily between the pads or something? (I do have a very large head, to accomodate the massive size of my brain, sigh!) -
so if considering one of those, I'd say try to test it on your boat first.  I use it half a dozen times a year or so, when launching or taking out the boat.  Have used it on the one trip on Missiniabi R - didn't like it any better then - I'd say it was adequate though.  Might be better with a lighter boat than the 65# of so of the rigged 'vouz.

Of course, I do very much prefer using my pack frame rig, like by a factor of 20 to one or more.  advantages are super easy carrying and balance on tough trails, and I can carry hands down, using one hand to balance the boat and using a paddle in the other hand as a walking stick for balance on logs or steep terrain; disadvantage is that it can be trickier to get the boat on the frame - best to just prop the bow up on a horizontal branch or in the croth of a tree, or between two close trees, then just duck under - if you will have someone else with you, then it is simple as pie to have that other person hold the bow of your boat up high while you duck under - cost is ? say $15 for a pack frame from a thrift store, and maybe $5 for a couple of brackets to attach to the top of the frame - you do need a frame without a crosspiece at the top - i.e like an "H" so you can attach the brackets to the top ends, and you need to measure the gap distance you will have on your seat so that you don't buy a frame wider than that gap.  Now, you know I do a lot of portages on my trips, and I would never consider changing to a "traditional" carry yoke for any of my boats - I enjoy the portages because carrying the boat is so easy.