Google announced a couple weeks ago that billing for Google Drive would move over to the Play Store subscription system. At the time it said this would happen sometime in January, but it looks like it’s already live for some people. Time to check your Google Play account page.
The subscription prices themselves aren’t going to change, you’ll just manage the subscription in a different place. It makes sense to move it, though.
The previously announced Google Play billing for Drive storage is already live for some was written by the awesome team at Android Police.