You can get many textbooks (I wouldn't recommend the typical school ones, but they can be useful, albeit more costly overall) for less than £30 that encompass most (if not all) specifications, with all sorts of whimsical tutorials and questions, including videos on a disc or online.
If I were you, I'd use that £80 to buy either your specifications textbooks, or the best darn book you can find. Just another note, Khan Academy is the best thing you could dream about, and it's free.