Ask HN: How do I sell an iOS app to a local dentist's business?

I recently began working as an iOS app consultant and in a few days I am meeting with the owner of a recently opened local dentist's office (someone I know referred him to me), who could potentially be my first client.

How do I convince him that an iPhone app will be worth more to his business than what I charge ($4,000/week)?

Most of the ideas for apps that I come up with for his business are neat and gimmicky, but they would not directly benefit his business by making/saving money, which would make it harder to sell to him.

What is an app idea for this local dentist's office that would save/make his business money?