I got a black tin case from Taobao.com which cost me RMB20 (=$4), with a cool appearance and exact fit, I think it's a economical solution for 505 protection.
Unfortunatetly, it's only available in China so far due to Taobao's operation and delivery concern, but u can also find such boxes with a size
20cm*14cm*1.8cm as the mentioned one to answer your needs.
http://item.taobao.com/auction/item_...999d5f117dadc2