I agree on the expense of it, here is one more supplier of it (not cheap) and other stuff.
http://www.jamestowndistributors.com...=305&page=GRID
Didn't see 1" thick stuff there but there is 3/8" in Starlight and it's about half price of Starboard but looks only available in gray.
Years ago I got ahold a couple of 2'x4'x 1/4" pieces of yellow PVC board and have yet to see it available in this area.
My only concern of using PVC is the product by it's nature is subject to temperature extremes. PVC will degrade in sunlight, producing a white chalky finish. It will also crack from twisting or stress. The other thing is it will shatter like glass near or below freezing temperatures.
A PVC board would be great for a lot of applications on a boat, keeping it's limitations in mind.