I've been thinking about getting one from these guys. I've bought other stuff from them (not for the Boxster) before. Their prices seem to be about the same as most. The Evolution fabric seems to be very good. I have a cover that I use on the Boxster made from this material. The cover is for a Mazda 626 and doesn't fit very well, so I'm considering buying one especially for the Boxster.
http://www.********************************************************************************************/sku/Toyota/Celica/Covercraft/Car_Cover/2005/GTS/4_Cyl_1-dot-8L/C59C80003WC.html?tlc=Car+Care