If the blu-ray is out of your price bracket then this seems to be a good price for the DVD box-set.
Starts at £34.99 with the Rakuten seller Entertainment Link. Then apply voucher code 25%COUPONFORYOU for a £8.75 discount (tested and working).
If you are already a registered member of Rakuten you should have had an e-mail with 500 free points (£5) to be used by end of Boxing Day. Apply these at the checkout stage.
This brings price down to £21.24.
If, like me you have existing points that you are happy to redeeem then you can bring price down even further (I have purchased for £14.75 delivered).
Possible Quidco or Topcashback as well.