Buy.com offers the Miccus ChargeBlock Battery Case for Apple iPhone 4, model no. CBI4C-20, for $19.99 with free shipping. That's tied with our expired mention from 10 days ago as the lowest total price we've seen. (It's also a current low by $37.) This 2.8-oz. case features a 2,000mAh rechargeable Li-Ion battery and four assorted faceplates.