I'm curious as to cost of the fancy shmancy seat too, I had to remove the backrest from my 09 Grandvista because with my leg length it was just uncomfortable on my knees and butt.
I shaved down the foam and put it back but the plastic frame that bolts on is the problem.
I just opted to leave it off for now, but there's another problem. Now I have three holes to cover or patch, but the riding is so much nicer!
I'd like to know where to find these optional seats, their cost, if they can be ordered online, they look pretty cool, but they don't look like they go back any farther than the factory butt rest.
All I've found on this topic here is really old posts, so I'm anxious to hear if someone chimes in on this.
Happy riding!