I doubt this cost is really the relevant one though. More importantly its the opportunity cost. Cable operators are limited in bandwidth and the number of channels they can carry at any given time. Getting rid of Ovation free's up that network bandwidth for another, more profitable network (or more HD channels etc...)
Ovation and Current both were at a disadvantage as independent networks. Larger network groups like NBCU, Scripps (food network) Viacom (Comedy Central & MTV) have a better chance getting a smaller network off the ground because of their increased leverage.
Hopefully at some point the cable operators will move to a Switched Digital Video[1] system which would free up bandwidth and allow for these smaller networks to get traction a bit easier, but its not going to happen soon and (hopefully) streamed internet networks will really start to flourish. Maybe the Ovations and Currents of the world will move this way sooner now.
They're afraid of negative reactions from viewers:
> Cable companies are also worried, said Burman, that they will lose more subscribers than they will gain by granting access to Al Jazeera.
Just having that "Al" in the name makes it sound like a terrorist network to a large fraction of Americans.
http://www.huffingtonpost.com/2011/01/30/al-jazeera-english-...
As for the politics of carrying an Al Jazeera owned channel in the U.S., it's a sad day for free speech.