iTunes offers downloads of Super Mario Run for iPhone and iPad (full featured) for $4.99 via the steps below. (Google Play charges the same for the Android version via the same process.) That's $5 off list and the lowest price we could find.

This in-game purchase unlocks all courses, all Toad colors, increased playable character numbers, and a number of bonuses. The game itself just got its "Remix 10" update, which randomizes the levels in interesting ways. So... let's-a go get this deal:
  1. Download the base Super Mario Run for iPhone and iPad for free
  2. tap "Tour" on the main screen
  3. tap "Special Price!" on the Tour screen to see the final price of $4.99