Calm is a fairly popular mindfulness and meditation app for both mobile and the web. They were Apple's App of the Year for 2017[apple.com]. While the app does offer some free access, unlimited subscriptions are either $13 a month, $60 per year or $300 for lifetime.
Educators around the world are eligible for a FREE lifetime account to use personally or in the classroom. Fill out the link below and they will get in touch with how to sign up.