Is Koh Tao expensive, or does that depend entirely on whether you dive?

The island has a reputation for being cheap that comes mostly from certification courses being competitive here. Take the diving out and the picture changes, because everything arrives by boat and the accommodation range is narrower than on the bigger islands. When you go decides whether the crossing is pleasant or grim, which we cover here: https://meetlocale.com/guides/andaman-vs-gulf What did a week there cost you, and were you diving or not?