The one from Cabrio World is made by GAHH. The other guys, PorscheKid, ddb, and others have that one. GAHH is based out of SoCal, they've had the glass window top out for a for a while.
AFAIK, the one from Convertible Tops Online just came out. Convertible Tops Online is a division of Nachos Auto Upholstery, also based out of SoCal.
BTW, Convertible Tops Online quoted my $550 for installation.
These are the only 2 shops in the US that I know of who make the glass window top replacement for older Boxsters.
When the GAHH top first came out, you could get it for like $650, but then the price crept up to the $900's. I think the CTO top will increase in price as it becomes more established, but not as much as the GAHH. I also think the GAHH top will come down in price a bit ---- capitalism, gotta love it.
Larez2