Amazon offers its Prime members the Diztronic Flexible Case for iPhone 5 for $11.90 with free shipping. (Non-members can spend $25 or more to qualify for free shipping; otherwise, shipping costs $5.04.) That's the lowest total price we could find by $3. This flexible case is made of TPU and measures only 1.4mm thick.

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.