Just thought i would throw this out there, some might find it useful.
In past when i have shipped some scion i go to this site
https://shop.usps.com/webapp/wcs/stores/servlet/CategoryDisplay?catalogId=10001&storeId=10052&categoryId=10000033&langId=-1&parent_category_rn=10000002&top=&sort=&viewAll=Y
i do not use the flat rate boxes but the regular priority mail ones it works well for me and its right around 5.00 to ship under a pound.
If you sell on ebay they also have a site as well that they send ebay priority boxes if you have an account here is link
http://ebaysupplies.usps.com/
totally free including shipping to your home.
Best Health