Mwave has the Datashell CBP-AT15 Robust Armor 15.6" Laptop Backpack (Steel Silver) for $30 with free shipping. Normally found for $50+. Compatible with laptops up to 15.6" and features water repellent nylon fabric and a hard outer shell. Flight attendants can't crush it no matter how hard they try.
Datashell Flying Shield 15.6" Laptop Backpack for $33 with free shipping