It depends on whether you use Google API.
Online Maps contains classes for working with most Google API web services.
You use them in this way:
http://infinity-code.com/atlas/online-m … ample.html
Online Maps does not contain hidden calls to these services, and you use it directly.
Quotas and prices you can find in the official documentation of the service that you use (if use).

I'm looking for the information about billing of the underlying service in the Online Maps asset purchased from the Asset Store.
Is it using the Google API?
Is there any charge for usage?

Thank you!