The GuitarRx App is free. Included with the app are 10 free riff lessons. In addition, bundles that contain riffs, licks and in some cases all parts of well known, commercial songs are available for purchase for a very modest price of between $0.99 to a few dollars.
To learn more about what bundles are available and their respective costs, please go to the Lessons Library page. In-app bundles can be found by selecting the "More" button in the GuitarRx app. Select a bundle and then follow the on-screen instruction in your smart phone to order.