Was in my local HMV and saw this in store for £10, reduced from £35, but looking online it's showing as £6.99! It has 4 discs so I'm guessing it's the 2 disc collectors version of the first film, along with the 2nd and 3rd films. The collectors edition of the first film is £3.99 on the HMV site so you get an extra 2 films for £3. Bargain if you ask me!
Edit: Just remembered, you also get 7% quidco with this as well making it around £6.50 :)