By comparison, Electronic Arts' own Origin store is currently selling the title for $20. No matter where Mass Effect 3 is purchased, players must register through Origin to play.
The deal is part of a wide-ranging PC download sale at Amazon that also includes markdowns on various single titles like Bastion ($3.75), Saints Row: The Third ($10), Deus Ex: Human Revolution ($5), and Lord of the Rings: War in the North ($5).
Numerous compilation packs are also on sale, including the BioShock Dual Pack ($10), the Dead Space Dual Pack ($8), the Dragon Age Dual Pack ($10), and the Firaxis Complete Pack ($20), among many others.
For the full rundown of discounted digital PC titles, check out the Slickdeals forum post.