https://www.xbox.com/en-US/live/d…r=shellnav
Marketplace.Xbox.com offers a Mass Effect 2 & 3 DLC Sale (Xbox 360, but also backwards compatible with XB1).
Mass Effect 2 DLC:
Arrival $3.49
Kasumi: Stolen Memory $3.49
Overlord $3.49
Lair of the Shadow Broker $4.99
Mass Effect 3 DLC:
Leviathan $4.99
From Ashes $4.99
Omega $7.49
Citadel (1 of 2) $7.49