Extorting the ticket sales will probably be good.

The problem is, it's something that must be done with killing as few people as possible as well as something that can't be made known to the public.

Which means that you're going to end up having to likely kill the guy you're extorting from (unless you can ensure he will in fact, keep his mouth shut about what happened).

Suppose you could just straight up steal them, but that's not extortion. That's just theft.

EDIT:
Or, you could try and get the idol to donate the money to another organization/give it to you willingly for whatever reason.