What's the story with buying DVDs?: Home libraries used to consist of books or records, or both. Now, with the ongoing upsurge in DVD sales, film libraries, large and small, are competing for shelf space in our houses. Advances in technology have made home cinema a reality through the ready availability of widescreen televisions and surround-sound systems.

The cinemas have fought back with massive screens, state-of-the-art sound and much more comfortable seating, but film companies are now generating more revenue from selling their movies on DVD than through the cinema box office.

Just as CDs signalled that vinyl was final, the advent of DVD has relegated videotape to the far corners of those stores that still stock movies on old-fashioned VHS. The quality of presentation on DVD is much sharper than on VHS, and the DVD format allows for masses of extras, such as commentaries by directors and actors, making-of documentaries and associated features.

For example, the recently released four-disc DVD of Ben-Hur, the Biblical epic that set a new record in 1959 when it won 11 Oscars, features the 214-minute film over two discs, with documentaries, screen tests, and as a special bonus, the restored version of the 1925 silent Ben-Hur with a splendid orchestral score.

That four-disc set contains far too much material for the average viewer to watch in one night's rental, and many special edition DVDs of classic movies are not available for rental, but for sale only. Meanwhile, renting a recent cinema release now costs up to €5.25 a night. Double that if you fail to return it on time, so you might as well have forked out a few more euro and bought the movie.

As with CDs, DVD movies generally cost significantly more to buy in Ireland than in the US, and while it is possible to purchase movies from online US sources, this may incur expensive postage charges and even VAT surcharges imposed by Customs. Bear in mind that DVDs bought from the US generally are in Region 1 format, which is incompatible with many European DVD players, although most modern DVD players can be "chipped" to enable viewing of Region 1 releases. Ireland, for the record, is in Region 2.

While the larger outlets of chains such as HMV and Virgin carry thousands of movies on DVD, the alternative of buying them from online retailers is a more relaxing way to shop and, in most cases, better value for money. Anyone who regularly purchases movies on DVD will be well aware of the remarkable disparity in pricing between different outlets.

Picking a random selection of 10 titles recently, I checked out what they cost at three Dublin stores - HMV on Grafton Street, Tower Records on Wicklow Street and Virgin in Dundrum Town Centre - and on the four websites I use most often to buy DVDs - www.play.com, www.sendit.com, www.blahdvd.com and www.cd-wow.com.

None of those websites charge for postage on deliveries to Irish addresses, and all four offer prices in euro at the click of an icon. Play and Sendit are particularly user-friendly, easily navigable and with ample information on the formats and contents of their wares. All four have sections for bargains, hundreds of them, which can make for an enjoyable few hours of shopping to build up a home film library.

The two-disc special edition of The Chronicles of Narnia: The Lion, the Witch and the Wardrobe, the biggest hit at Irish cinemas last Christmas, varies in price from €20.99 at Sendit to €29.99 at Virgin, while Cd-wow.com is the most expensive online outlet, charging €26.99. However, Cd-wow.com offers the best value on the two-disc special edition of the latest King Kong, selling it for €16.99, whereas it's €22.99 at Virgin and HMV, and €29.99 at Tower Records.

The best deal on the awards-laden Brokeback Mountain is €17.49 at Sendit.com, and the most expensive is Tower Records at €26.99. David Cronenberg's recent, critically acclaimed A History of Violence ranges from €14.49 at Play.com to €19.99 at Tower to €26.99 at both Virgin and HMV. Now available on DVD for the first time, John Huston's wonderful swansong, the adaptation of James Joyce's The Dead, costs €11.99 at Sendit.com, €12.99 at Play.com €14.99 at Virgin and €17.99 at HMV.

Foreign-language movies usually cost more than mainstream material, presumably because the market is more limited and perhaps because distributors believe interested viewers can afford the mark-up. Recently released on DVD for the first time, Krzysztof Kieslowski's emotional drama, The Double life of Veronique costs €22.49 at Sendit.com and €23.99 at Play.com, but it rises to a whopping €38.99 at HMV and €39.99 at Virgin.

Television series constitute one of the fastest-growing areas of DVD sales, with viewers willing to pay substantial sums to own series shown for free on TV. I can certainly recommend the experience of immersion in an entire series of a thriller such as 24 over a concentrated period of three days, when one only has to wait a minute and not a week to catch the outcome of every cliffhanger ending.

The first series of the ratings hit, Lost, is available in a box set that varies substantially in price, from €47.99 at Sendit.com and €51.49 at Play.com to €69.99 at Virgin and €79.99 at Blahdvd.com. The complete seventh series of The Simpsons - in a limited edition box shaped like Marge's hairstyle - costs from €36.99 on Cd-wow.com to €59.99 at Tower.

In terms of box sets, the best value online for Monty Python The Movies, featuring the troupe's five comedies, is on Sendit.com at €20.99, whereas it costs €51.49 at Play.com. In stores its cost ranges from €29.99 at Tower to €39.99 in Virgin. And The Pink Panther Film Collection, containing the five movies starring Peter Sellers and with a bonus disc of extras, costs from €49.99 in Virgin to €79.99 on Play.

The message is clear. If you've got the time, shop around. It's well worth it, and you may well pick up some excellent bargains along the way. Now if only some outlet would provide custom-built shelving units to accommodate the bulging DVD libraries of serious collectors . . .

• All prices are correct at the time the comparison was compiled. Where titles in this price survey were not in stock at the time of the survey they are marked n/a (not available)