Click on the airline name to go to their media rate page
Look for "Media Bags" almost at the bottom.
Look for "Large Media Camera Equipment" about 5 lines down.
A bit of a pain to find: At the bottom of the page, look for "Sports Equipment & Special Items", then in the opened window
click on "Sporting Equipment & Special/Fragile Items PDF", which will download the PDF.
Then look for "Media Equipment".
The easiest of all these airlines, takes you right to the section.
Please note that airlines change their minds on the rules and 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.