As one of its daily deals, Best Buy offers the Paranormal Activity Trilogy Gift Set on Blu-ray Disc (pictured) for $13.99 plus $2.99 for shipping. That's the lowest total price we could find by $1. It includes Paranormal Activity, Paranormal Activity 2, and Paranormal Activity 3 on three discs.
Of note, it's also available on DVD for $9.99 plus $2.99 for shipping. That's the best price we could find by a buck. Both deals end today.