Amazon offers its Amazon Prime members the Kingston 16GB Ultimate X SDHC Class 10 Secure Digital High-Capacity Card, model no. SD10G2/16GB, for $18.98 with free shipping ($1.25/GB). (Non-members can spend $25 or more to qualify for free shipping; otherwise, shipping costs $8.02.) That's the lowest total price we could find by $1, although we saw it for $1 less a month ago.

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.)