eXpansys offers the Amzer Organics Case for Apple iPhone 5 in Black, model no. AMZ94810, Slate, model no. AMZ94809, or Sand, model no. AMZ94808, for $9.99. Coupon code "AMZER15" cuts it to $8.49. With $3.99 for shipping, that's $1 under last week's mention and the lowest total price we could find for this case by $2. This case is purported to be 100% compostable and biodegradable.
Update: newegg now offers this case in Sand for $9.95 with free shipping.