Well after getting the VFR my lady wanted a backrest so she felt more comfortable. However I just couldn't justify $250 on the corbin piece. So I decided to make my own.
Started off with some 5/8" square bar, and some 3/16" flat plate steel. I then cut the design into the steel for the backrest and cut about a 12" length of the square stock. Then I put the square stock into the corbin seat slot and had my lady sit on the bike so that I could see what angle to bend the square stock at. Turned out to be about 10 degrees for her, but see what your passenger wants. 0 degrees is almost straight up FWIW. I then put the flat plate in a roller and rolled a bit of a curve into the flat plate, then welded together. Her brother-in-law owns a hot rod upholstery shop, so he ordered the CF look vinyl to match the seat and covered it for me. Due to the awkward shape of the backrest, he had a bit of a pooch where he finished the bottom of the cover, but for free I wasn't expecting much. Once I got it back, I put it in the corbin slot and punched a marker spot in the square stock where I drilled and tapped for a 1/4-20 bolt to secure it in place. I use a thumb screw, lock washer and a fender washer to spread the load and not crack the seat pan and be able to take off with out tools. This setup has worked great for us and hopefully it can save you a bit of $$ too.
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She loves the new set up and says that it makes her feel much more at ease while on the bike. I sat on the passenger area and put all of my weight on the back rest and I couldn't budge it, sturdy as a rock. Fabrication wise it took about 2 hrs to make, so with minimal time and skill you too can have a cheep backrest.