Copywrite Protected Music Use

I have had to explain to clients (Internal/External) the reasons why they cannot have Van Halen music on their commercial, video, film, presentation, corporate event etc etc... more times than I can count as I am sure most of us have. But I have a group inside my current company who just will not take this as an answer. I have given them links explaining at nauseam the reason and legalities. They keep coming back asking "well, how much would it actually cost"? Just so I can settle the case and give them a somewhat ballpark number - has anyone ever tried to secure the rights to a popular song either for a film, commercial or even a giant corporate event? Not an indie artist who maybe scored a short film for a grand or so but more like a Bob Seger's "Like a Rock" for instance - I just want to show them a solid example of what is involved and the cost. Also it would be cool to hear about. Thank You to anyone who will humor me!