AccessoryOne via Amazon offers Amazon Prime members the Griffin Elan Form Hard-Shell Leather Case for iPhone 4, model no. GB01763, for $5.05 with free shipping. (Non-members can spend $25 or more to get free shipping; otherwise it adds $5.20.) That's the lowest total price we could find by $5. It features a perforated leather outer layer.

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 there is a waitlist for Amazon Mom.)