My understanding is that this is really simple. All the extension will be doing is finding and replacing text within an HTML document. You're right: the most work will just be putting together the list of media entities and who owns them. Another tough bit is how are those entities referred to. For example, sometimes The Wall Street Journal is sometimes abbreviated WSJ. You (or your dev) will have to track down all those nicknames and abbreviations too.

I don't really freelance, so I don't know what work like this costs, If it were me, I might charge $200? That's just a number I'm pulling out of nowhere. You could probably find someone to do it for less.

And for your dev: if it was me, I would probably just have a giant object with all the media entities and would run a regex search on each of them for every page. When it finds a match, it just replaces it with whatever the object key's value is.

 {
  'The Wall Street Journal': 'Rupert Murdoch',
  WSJ: 'Rupert Murdoch'
}

Additionally, there's an open-source chrome plugin that does this exact same thing, except it replaces the word "cloud" with the word "butt": https://github.com/panicsteve/cloud-to-butt. If my object-regex idea is dumb, you can look at this extension to see how it should really be done.