In the film 'Mary Poppins', how much was a bag of birdseed?

I watched this film recently for the umpteenth time, my wife had never seen it. I've got to get her to watch Chitty-chitty-bang-bang next.

That was such an annoying song and movie. I was just kid but I knew "annoying" when heard it or witnessed it.

Now I've got the tune stuck in my head.