I recently learned that The Book Depository (a British online bookstore recently acquired by Amazon) has the Longman Dictionary of Contemporary English for about $24 with free worldwide delivery. This is the lowest price, online or offline, that I’ve seen for this excellent dictionary. Note that for this price you get the DVD only (no paper book). But who has the time to leaf through a huge book, right?
Of course, the first thing you should do after installing the LDOCE is download Taku Fukada’s unbelievable LDOCE5 Viewer which will turn your LDOCE from mediocre to amazing.
If you also need the book version for some reason, The Book Depository has the paperback+DVD for about $44 (free worldwide delivery). Amazon.co.uk has it for £23.79 (about $37) but delivery is not free, so it would probably end up costing more. (However, Amazon.co.uk has free delivery to some European countries if your order comes to more than £25, so you could order something else in addition to the LDOCE in order to qualify for free shipping.)
Thanks to commenter “michau” for the tip about The Book Depository.