I don't doubt that an international association like the Red Cross has administrative overhead. It is reassuring thought that overall reports  seem to be positive.
If that argument is not enough, I'd argue further: we cannot know for sure how (or if) our contribution will make it to those that need it, but I'd rather donate now and research later than postpone the donation "just until I find the ideal charity" and then forget about it. The Red Cross has been around for around a hundred years, though, so I'd say that's good enough when it comes to trusting a random association to coordinate at a global scale.
Disclaimer: I donated to the Red Cross