Premium subscriptions renew automatically unless you cancel it.
Accepted payment method for Premium subscription in Google Play is Credit card
Other payment methods are not available. e.g. Google Play balance can't be used to pay for Premium subscription, Because of its renewable nature.  

The price depends on your region and currency. You can find your local price in the app. 

With the Subscription you'll get Premium maps and an ad free app.

More info about
Google Play subscriptions here.
Accepted payment methods in Google Play here