Next best is £24.99 at Zavvi (in-store). You can only get this in-store or on Zavvi's site; all other retailers are the standard 4-disc version. This version includes bonus discs for each film, which comprehensively cover the creation of all the films, including documentaries, deleted scenes, promotional material, outtakes and more. This also includes the harder version of Die Hard 4.0, which is not included on the 4-disc version, and adds in swearing and gore (improving the film in my eyes).
Best price for buying seperately:
Die Hard: 2-Disc Special Edition - £5.99
Die Hard 2 - Die Harder: 2-Disc Special Edition - £4.99
Die Hard with a Vengeance: 2-Disc Collector's Edition - £2.99
Die Hard 4.0: Ultimate Action Edition - £6.98
Die Hard (2 Disc Edition): In this high-rise, high-stake Die Hard series opener, Detective John McClane heads for Los Angeles to spend the holidays with his estranged wife, Holly (Bonnie Bedelia). But while McClane waits for Holly's office party to end, terrorists take control of the building. And as their sinister leader (Alan Rickman) and his savage henchmen round up hostages, McClane gets ready to launch at one-man war - as only McClane can!
Die Hard 2 - Die Harder (2 Disc Edition): Off-duty in the nation's capital, John McClane spends Christmas Eve battling a team of terrorists and their murderous leader (William Sadler), who have taken over a major international airport, while he copes with an inept airport police chief (Dennis Franz) and the knowledge that his wife (Bonnie Bedelia) is trapped in a plane desperately low on fuel, circling overhead!
Die Hard - With A Vengeance (2 Disc Edition): Exploding with special effects, comedy and nonstop thrills, the third chapter of the Die Hard series finds McClane the personal target of a terrorist (Jeremy Irons) determined to blow up New York City if he doesn't get what he wants. Accompanied by a reluctant civilian (Samuel L. Jackson), McClane engages in a tense battle of wits with a psychopathic genius in this thrill-a-minute adventure that grabs you and doesn't let go!
Die Hard - 4.0 (2 Disc Edition): The best is back in action in the latest instalment of the pulse-pounding, thill-a-minute Die Hard action films. New York City detective John McClane (Bruce Willis) delivers old-school justice to a new breed of terrorists when a massive computer attack on the U.S. infrastructure threatens to shut down the entire country over Independence Day weekend. Locked and loaded with real stunts, genuine humor and nonstop excitement, Die Hard 4.0 is the most explosive action movie of the year. Yippee-ki-yay!