If you're a thrifty shopper, your best bet is this Corsia Rucksack. It's a popular piece, while not very costly. Another savvy option is this Piquadro Backpack. It's a product you're bound to love which also doesn't cost too much. You may also want to look at this Parentesi Backpack. This item is not expensive either, but it will make a difference in your wardrobe.
If you're looking for an item in the middle of the price range, you're in luck with this Frye Backpack in stock and waiting for you. You are bound to love this product. You can also take a look at this Piquadro Backpack. It's an attractive option both price and quality-wise. And do check out this Rucksack! It's a very popular item and good value for money.