Groupon offers the Serious Sam Collection for Xbox 360 for $11.99 plus $3.99 for shipping. (
Amazon has it for a penny less for Prime members.) That's $2 below our February mention and the lowest total price we've seen. (It's a current low by $4.) It includes Serious Sam HD: The First Encounter, Serious Sam HD: The Second Encounter, Serious Sam 3: BFE (plus Jewel of the Nile DLC pack), and Serious Sam: Double D XXL, plus bonus content.