if you don`t mind R1 you can get it from DVDSoon for about £17.50 (less if you are in their loyalty scheme) - dangerously close to the £18 customs limit so you could be taking your chances on the exchange rate movement.
talking of the loyalty scheme they are currently offering 2 free DVDs/DVD sets if you sign up before the end of the month. It costs about 50 canadian dollars (somewhere between £20 and £25); among the free DVD sets 24 Season One caught my eye - I don`t know about the other DVDs but the offer could possibly pay for itself.