CTCStore offers Amazon Prime members the Acase Matte Screen Protector for iPhone 4 / 4S 3-Pack for $9.49. Coupon code "U75OZ5TD" drops it to $3.25 with free shipping. (Non-members can spend $25 or more to qualify for free shipping; otherwise, shipping costs $5.03.) That's the lowest total price we could find for a similar 3-pack by $1, although we saw one with front and back covers for the same price five days ago (since expired). It includes three front screen protectors. Coupon expires December 22.

Orders placed by December 21 at 11 pm ET using Amazon Prime are guaranteed to arrive by Christmas. Amazon Prime membership is $79 per year; however, Prime is free for college students for six months, and free for parents and caregivers for three months. (Note that currently there's a waitlist for Amazon Mom.)