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 Google Storage page is only for the shared Google storage subscription, but the Play Store has all the other subscriptions billed through Google (eg. Play Music, apps, etc). Here's the email Google sent about the change a few weeks back.
One notable upshot here is that you can use Google Play credit to buy Drive storage after the change. That's handy, especially if you've been hoarding Opinion Rewards credit. If you don't yet have the subscription option in the Play Store, give it a few days. This is a slow rollout.