Lenovo takes an extra 20% off a selection of its Lenovo ThinkPad cases via coupon code "BACKTOSCHOOLCASE". Plus, all orders bag free shipping. Deal ends August 31. A couple of best bets, with prices after coupon:
Lenovo ThinkPad 16" Professional Slim Topload Case for $39.99 (low by $8)
Lenovo ThinkPad 16" Professional Roller Case for $135.99 (pictured, low by $18)
There's a less expensive way, and then there's the way that works for you. The two may not be the same.