Amazon offers downloads of Back to the Future Vol. 1: Untold Tales and Alternate Timelines Digital Comic for Kindle & Comixology for 99 cents. (Google Play charges the same.) That's the lowest price we could find by $6. It includes the first five issues of the Back to the Future comic series.

Also available are downloads of Back to the Future Vol. 2: Continuum Conundrum Digital Comic for Kindle & Comixology for 99 cents. (Google Play charges the same.) That's the lowest price we could find by $4. It includes issues six to 11 of the Back to the Future comic series.