Walmart offers the Ozark Trail 25-Liter Roll Top Backpack in Gray for $19.65. Choose in-store pickup to avoid the $5.99 shipping fee. That's tied with last week's mention, $10 off, and the lowest price we could find. It holds a 15" laptop, is hydration compatible, and features an internal sunglasses pocket, bike light attachment, four side buckles, padded back and straps, and adjustable sternum strap.
There's a less expensive way, and then there's the way that works for you. The two may not be the same.