eBags via eBay takes up to 75% off a selection of laptop and messenger bags, with prices starting from $9.34. (Although the banner states up to 50% off, we found deeper discounts within. Prices are as marked.) Plus, most items bag free shipping. A couple of best bets:

• Bellino Rolling Computer Backpack for $30.59 (low by $5)
• SwissGear Travel Gear 18" Laptop Backpack for $38.24 (pictured, low by $5)