Balance: Meditation is an app similar to Headspace / Calm / 10% Happier. They are giving away a free-year long trial atm, then $48.99/yr afterwards but you can cancel early. Just use the app, create an account, go through the first time setup and select one of the locked options and you will be presented with the IAP option.
You can do the free trial and cancel right afterwards (in Settings -> iCloud Account -> Subscriptions) to ensure the subscription is still active yet you don't have to worry about forgetting to cancel it next year.