We have 2 Roubaix bikes.

I have a Comp frame that the shop built up with Chorus components. The Comp frame isn't usually sold alone, but they had this one from a trade-out with a Pro frameset and I got for $1200. According to the shop, it is the exact same as the Pro frame except the finish.

The S-Works Roubaix is the one with the pretty 3K weave finish. Shannon got one this year and it is very sweet. BTW, "3K" refers to the cost of the frameset.

Specialized sells the Roubaix Pro (and the S-Works) as a frameset for those people who want to build up the bike with Campy or their own choice of components.