I've been looking at doing this as well. As I'm sure you already know, there are several companies out there selling them.
I found one that at least seemed to have a good reputation from the people buying them. I have an '07 Chevy Cobalt LT that I use as an occasional daily driver when I don't want to get the H2 dirty and I actually found this company on the Cobalt forum.
I haven't ordered from them yet, but a complete set was like about $170. I think they were from
www.visionbulbs.com
The way I looked at it, was that for the price of SilverStar Ultra's, it wouldn't be too much more to just go with these and they are true HID's.