Click on the airline name to go to their media rate page
Look under "FRAGILE, BULKY & OTHER ITEMS" for Media Bags, about halfway down.
Look for and click on "Audio or visual equipment" at top.
Look for "Large Media Camera Equipment" about 5-6 lines down.
I am unable to locate anything about Media Bags.
The easiest of all these airlines, takes you right to the section.
Please note that airlines change their minds on what to charge on a regular basis.
Also note that the webmasters for these airlines move/change the URLs for media bags too.
So the links may not be correct.