Amazon has the adidas Team Issue II Medium Duffel Bag (Jersey Onix Grey) for $25 with free shipping. Has 6.5" shoulder drop and water-resistant base.
Bags & Travel - Best Deals and Sales at Amazon
$25 retail: $50Report
Amazon has the Case-It Laptop Backpack with Hide-Away Binder Holder (BKP-102 PURG, Purple Grey) for $12 with free shipping on $25+ or with Prime. Walmart has it for the same price with free in-store pickup. Fits 13" laptops.
$12 retail: $40Report