By the time you track down the material from Bayliner, pay all of those shipping charges and what not it would be cheaper and faster to stay with a local upholstery shop. The material can be ordered off the net from several different places. I've dealt with these folks before and they are really good at what they do :
http://www.garysupholstery.com/.
However I would definately do some pricing and see which way would be the least expensive. Quality wise I think you will see that most of the aftermarket items will be a little better.
Jerry