If you're after a thrifty option, your best bet is this ASOS DESIGN Backpack. It's a popular product, while not very expensive. Another smart option is this Mi-pac Backpack. While the price is rather reasonable, be sure that this product will become an excellent addition to your wardrobe. You may also want to look at this Accessorize 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, we recommend considering this Manu Atelier Rucksack. While the price is very reasonable, this item is an easy wardrobe update. It's also worth taking a look at this Anya Hindmarch Backpack. This piece is extremely popular and, just as importantly, not too pricey. And do check out this Mansur Gavriel Rucksack! It's a very popular item and good value for money.