9steals via Amazon offers Prime members the SHARKK Aluminum Credit Card Wallet
in Red or Blue for $3.99
with free shipping
. (Non-members can spend $25 or more to qualify for free shipping; otherwise, shipping costs $5.17.) That's the lowest total price we could find for such an aluminum wallet by $1, although we saw this for a buck less a month ago (since expired). It claims to protect credit and other cards from RFID scanners and is water-, stain-, and impact-resistant.
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.