NEW YORK (CNN/Money) - Which movie has the best payback this summer? Is it "The Hulk," "Charlie's Angels 2" or "The Matrix: Reloaded"?

The answer: none of the above. The movie with the best return on investment is a low-budget independent film called "28 Days Later."

The British horror film, about killer zombies that spread a deadly disease called "Rage," first surfaced in major cities on a limited basis June 27 and then rampaged to theaters across the United States, taking in more than $40.3 million at the domestic box office as of Aug. 3.

This summer's big-budget films open huge but fizzle quick. CNNfn's Jen Rogers takes a closer look at some of the sleeper hits. Play video (Real or Windows Media)

The gross doesn't seem significant compared with even the sour $38 million opening for "Charlie's Angels 2: Full Throttle." But for a film that only cost $8 million to make, it's a return of 403 percent.

Directed by Danny Boyle and produced by Fox Searchlight Pictures, "28 Days Later" has captured a cult following -- mainly among teen-age boys and men under 30.

The success of the film provides a clear contrast to a gloomy summer box office full of high-budget mainstream films. Some experts credited Fox with outwitting major studios by using a smart and cost-efficient marketing campaign.

Besides Warner Bros.' "Matrix" and Disney's "Finding Nemo," which has surpassed "The Lion King" to become the biggest-grossing animated movie of all time, many big-budget standouts this summer only fared well during their opening weekends, but not beyond as fierce competition cut into ticket sales.

Some even took a gruesome punch after the first weekend.

"Hulk," for instance, tumbled more than 70 percent after its opening weekend. "Angels" also got throttled, with a decline of 60 percent in the second weekend. "Tomb Raider 2," with a reported budget of $90 million, took in only $22 million in its opening weekend.

"There hasn't been a lot of positive word-of-mouth on the mainstream films this summer," said Paul Dergarabedian, president of Exhibitor Relations, a box-office tracking firm. "Great marketing, huge production spending can probably get you a mega opening, but beyond that, it's up to the moviegoers to spread the word," he added.

A lot of audiences are turning to "28 Days Later" or some of the other smaller films to get their fix for some quality films, he added.

Fox Searchlight chose not to follow the traditional marketing format for "28 Days Later." The studio stayed clear of expensive television commercials and flashy magazine covers.

Instead, Fox shifted focus to a more cost-efficient advertising campaign on the Internet.

Fox Searchlight's horror flick "28 Days Later" took in more than $37 million 28 days after its release.

"TV commercials are expensive," said Steven Yee, vice president and general manager of AOL Movies and Moviefone. "How many people can you call after watching a good trailer on TV? But it's quick and easy to send a movie clip to a group of friends through e-mail or IM [Instant Messenger]."

"28 Days Later" quickly caught on through the Internet campaign, and its popularity spread viciously across the boundary-less Web-based world of horror film fans.

Fox reportedly spent $1 million on banner ads to attract movie buffs on sites like Moviefone.com and Yahoo!. Fans can also view a six-minute trailer on Apple.com or the film's official site. (www.28dayslater.com)

"[Fox] used a targeted approach. It reminds me of the marketing for 1999's 'The Blair Witch Project,'" Yee added, referring to one of the most successful independent films.

But appetite for quality indies was not truly awakened until last year's sleeper hit, "My Big Fat Greek Wedding," said Dergarabedian.

The romantic comedy, about a shy, klutzy Greek-American, opened the eyes of many to low-budget indies, said John McCauley, vice president of marketing for Loews Cineplex Entertainment.

"My Big Fat Greek Wedding," the sleeper hit of 2002, earned over $240 million on a production budget of $5 million.

"Greek" cost about $5 million to make but took in more than $240 million at the U.S. box office. That translated to a return of 4,728 percent for distributor IFC Films.

"The general public, which usually prefers big blockbusters, is now willing to give smaller films a chance," McCauley said. "They are not only popular in big cities anymore."

Some indies may not have done as well as "Greek." But even a film like "Better Luck Tomorrow," which only sold tickets totaling about $3.8 million, can brag of a great return when the film only cost $250,000 to make.

In addition to banner ads and online trailers, Fox sent out free merchandise, such as baseball bats, to attract male audiences.

The studio even added an alternative ending, beginning July 25, to satisfy fans who thought the original ending was too upbeat and conventional.

"The second ending worked in a way to win back repeat audience," McCauley said.

An alternative ending of a movie typically only becomes available on DVDs, but "giving a new ending to boost ticket sales while the movie is still in theaters is an innovative marketing strategy," McCauley said. "They really went after the core audience, and that's why it worked."

Fox Searchlight, the art film division of Fox Entertainment Group (FOX: Research, Estimates), declined an opportunity to speak with CNN/Money about the film.

"Matrix" is produced by Warner Bros., which is owned by CNN/Money and AOL's parent AOL Time Warner (AOL: Research, Estimates). "Tomb Raider" was released by Paramount Pictures, a unit of Viacom Inc. (VIA.B: Research, Estimates). "Better Luck Tomorrow" was produced by MTV Films, also owned by Viacom.

"Angels" was produced by Universal Pictures, a subsidiary of Universal Vivendi (V: Research, Estimates). "Nemo" and "Lion King" are all films from Walt Disney Co. (DIS: Research, Estimates).