Alex Garland has learned a few things in his years as a science-fiction screenwriter: namely, that money doesn’t always help.

Garland is now making his directorial debut with the acclaimed science fiction film “Ex-Machina,” after earlier scripting the influential zombie thriller “28 Days Later” and seeing his first book, “The Beach,” turned into the Leonardo DiCaprio adventure. The 2007 Danny Boyle-directed space thriller “Sunshine,” which Garland wrote, particularly drove home the lesson.

“The thing I really felt about ‘Sunshine’ almost while we were making it, is that we were spending too much money,” says Garland. “When you’re spending that much money, either consciously or unconsciously, you start to think about recouping. You start to think about the business of film and trying to make it entertaining or trying to adrenalize it at moments when it’s the wrong thing to do.”

Garland’s “Ex-Machina,” which opens in theaters April 10, was made for $15 million, not the $50 million it took to make “Sunshine,” a philosophical journey to the sun that eventually dissolved into more of a monster movie. “Ex-Machina,” however, holds its trance throughout the tale of a young computer programmer (Domhnall Gleeson) who flies to the remote lair of a tech billionaire (Oscar Isaac), and is introduced to a very realistic artificial intelligence (Alicia Vikander).

“The one thing I do know is that I really, really want creative freedom — not just for me but the people I’m working with,” says the British writer-director. “You need to be Christopher Nolan to have creative freedom at that level. That’s what, like, two or three people in the world.”

Instead of fighting those odds, a new generation of filmmakers is breathing fresh life into the often over-commercialized genres of sci-fi and horror. A regular diet of big-budget releases have helped stagnate genre thrills by over-relying on visual-effects spectacle (“Jupiter Ascending,” “After Earth”), while mainstream horror has been overrun by gimmicky shlock (the “Paranormal Activity” series) and familiar retreads (“I, Frankenstein”).

But many of the most exciting horror and sci-fi films in recent years — “Under the Skin,” “The Babadook,” “Her,” “Upstream Color,” the “Black Mirror” miniseries — have come from independent filmmakers working with small or even skimpy budgets, who prize creative control in genres where final cut is scarce.

Janet Pierson, head of film at South By Southwest, where “Ex-Machina” premiered, has regularly programmed inventive genre fare. While she’s witnessed steadily intrepid sci-fi and horror for years, she sees a larger shift.

“What I’ve noticed is that the young people that come in here, particularly more and more of the women, their first love is genre films — which is a real change, which is something that didn’t exist before,” said Pierson. “I come from the more traditional art-house generation.” 

David Robert Mitchell, writer-director of the indie horror sensation “It Follows,” is a kind of combination genre-art house filmmaker. His first movie, “The Myth of the American Sleepover,” was his version of a teen drama that portrayed the quieter moments of adolescence, rather than the melodramatic extremes usually depicted in the genre.

“It Follows” is his stab at horror. The DVDs he pulled off his shelf in preparation make a respectable horror syllabus: “Nosferatu” (the original and the Werner Herzog version), Romero, Cronenberg, Polanski, the classic Universal monster movies, the Hammer classics, “The Shining” and many more.

“There’s a bunch of us that grew up watching what are now seen as classic horror films,” says Mitchell, a Michigan native. “That’s probably affected a lot of us to, if not update them, be inspired by them.”

Mitchell’s deep appreciation of the genre is self-evident in “It Follows,” an atmospheric suburban teenager thriller with a synthesizer score evocative of John Carpenter. “It Follows” has crossed over from art house to mainstream: it expanded last weekend to some 1,200 theaters, despite earlier plans for video-on-demand. It pulled in $4 million at the box office, about twice its budget. 

While he acknowledges “more money would definitely be helpful” and that he may later be interested in directing bigger studio films, “my intention is to kind of take my time with that,” says Mitchell. “And that’s by choice.”

“Ex-Machina” and “It Follows” both create suspense by relying on acting and atmosphere. “It Follows,” in which an unseen, unknown entity is passed like a sexually transmitted disease, works like “Jaws” or “The Evil Dead”: What we imagine is more fearful than anything a movie can physically represent. “Ex-Machina” has the distilled feel of a chamber piece: It’s all questions and mysteries to unravel, none of the fat of special effects set-pieces.

“What that stuff does is it takes the heat off characterization and themes and story,” says Garland. “What a chamber piece does is it leaves you nowhere to hide.”