I have a Covercraft fitted cover on my Kawi 550SX and it fits like a glove. From Covercraft, looks like the 96-18 Superjet in Ultratect fabric (XW837UL) is $105 and Sunbrella fabric (XW437D1) $130.
I have Yamaha OEM covers on my Superjets. They are Surlast Fabric material, made by Commercial Sewing and fit perfect.
Black OEM cover MWV-CVRSJ-GY-12 $122 shipped
from ebay. And $132
from Amazon. Current model.
Blue OEM cover MWV-CVRSJ-BL-08 are older and around ~$165.
I have a black MWV-CVRSJ-BK-YL and blue MWV-CVRSJ-00-98 but they are older part numbers.
At $122, OEM is the way to go for sure. My blue cover is tired and will be replaced with another OEM.