If you're on a thrifty mission, your best bet is this Weekday Backpack. It's a wonderful product, while not very pricey. Another strong contender for your wardrobe is this Missguided Backpack. While the price of this item is not too high, it will definitely attract a lot of attention. You may also want to look at this ED Ellen Degeneres Backpack. This item is not expensive either, but it will make a difference in your wardrobe.
If you're a bargain shopper, you're in luck with this Marc Jacobs Backpack in stock and waiting for you. You most certainly will love this item. You can also take a look at this Marc Jacobs Backpack. It's an attractive option both price and quality-wise.