iTunes offers the Autodesk SketchBook Pro Upgrade for iPhone and iPad for free. (Google Play has it for Android and Microsoft Store has it for Windows for the same.) That's a savings of $85 per year for the full version of this sketching/art app. (The app has always been free; however, this is the in-app upgrade that is now free.)

Note: Sketchbook has it for your Mac or 64-bit Windows for free, too!