Sony Pictures Worldwide Acquisitions’ recent pickup of SXSW premiere “Attack the Block” for Sony’s Screen Gems may seem unusual — it reps an instance in which one of Hollywood’s biggest studios has nabbed a low-budget U.K. film with no big stars after its debut at a festival not known for big sales tiles.

The move, however, is part of a growing trend among studios taking more manageable risks on small finished films — often genre titles — with a potentially big upside. With bigger distribs and even majors becoming more open-minded about picking up films from more diverse places (such as Lionsgate with “The Last Exorcism” just before its Berlin market debut), it indicates the potential for Tribeca’s long-gestating market to produce its first sale to a major outfit.

Some recent examples include SPWA partnering with FilmDistrict to acquire horror pic “Insidious” at Toronto, and Lionsgate nabbing the Iraq-inspired gangster drama “The Devil’s Double” at Sundance.

Pacts for finished (or near-finished) low-budget film buys are also being inked outside fests, such as recent horror purchases William Brent Bell’s “The Devil Inside” by Paramount (brought to them by producer Lorenzo di Bonaventura); and Barry Levinson’s “The Bay” by Lionsgate.

“While major stars will always be a factor in movies, movies are more buzz- and word-of-mouth driven than ever before, and don’t always need star power to open,” notes SPWA prexy Steve Bersch. “That’s certainly reflected in our interest in ‘Attack the Block,’ a film we feel will be word-of-mouth driven.”

The trend of more majors making minor investments can be attributed to several factors: the changing tastes of audiences, the quality of indie product and the current economics of the film industry. The breakthrough seems to have been Paramount’s “Paranormal Activity” — picked up from the 2008 Slamdance Film Festival after its debut at the 2007 Screamfest Horror Film Festival. The $15,000 film’s $193 million worldwide gross helped convince the studio to launch Insurge Pictures for microbudgeted indie releases. Lionsgate followed suit with a plan to produce up to 10 films a year with budgets of less than $2 million.

“You have to believe enough in the movie that it justifies spending P&A, regardless of the budget,” notes Lionsgate acquisitions and co- productions prexy Jason Constantine. “The ultimate compliment a distributor can pay a filmmaker is to say, ‘We think you did such a great job with this movie you made for $1 or $2 million, that we’re going to put up $20 or $24 million to release your film.’?”

Constantine cites the success of “The Blair Witch Project” (from now-defunct indie Artisan Entertainment) as a turning point in Hollywood looking to high-concept, low-budget genre hits. (Lionsgate, which has grown from an indie to a minimajor, kept the approach going with the “Saw” series and other horror hits.) But several new factors have led big studios to jump in the game.

One key reason for the surge in low-budget buys — which may work in the favor of Tribeca, SXSW and other emerging markets at film festivals — is the increasing number of buyers looking for wide-release product.

In the past few years, Summit, Relativity, FilmDistrict, Open Road, the re-energized Weinstein Co. and others have emerged with a need for more films releasable to mass audiences, an arena once primarily left to studios and their specialty divisions. The new competition has led them to look in unusual places for less obvious films, along with smaller investments that will allow them to mitigate risk.

“When you combine the fact that smaller-budget, nonstar movies tend to be working with the number of distributors now playing in that realm, both factors lead to a greater appetite for the product and more aggressiveness seeking it out,” notes SPWA’s Bersch.

At the same time, studios have scaled back or cut their specialty divisions, and find they have space alongside their tentpoles for smaller films with potentially big upsides. Paramount Vantage, for example, now exists mainly in name only, though many of its staffers with the skill set to release a limited number of specialty titles under the label (such as “Like Crazy,” acquired at this year’s Sundance) remain at the studio.

One might assume that improving digital technology has made it easier for indie film producers (like Studio Canal, which is behind “The Last Exorcism” and “Attack the Block”) to produce slick films that look much more expensive than they are, and that a studio wouldn’t feel embarrassed to put its name on. This may be true in some cases, but surprisingly, the opposite has also occurred: Audiences are more willing to accept films that look more DIY.

“With all these found-footage horror movies, they’re used to the genre,” says one major studio exec with success in the arena. “And if you look on television, practically everything’s a reality show. ‘Jersey Shore,’ ‘The Real World’ — none of that looks great — it’s all handheld, shaky cameras. That’s what people are used to.”

All this means more attention is being paid to potentially fertile ground like Tribeca than ever.

In fact, for all the studios’ willingness to pick up nonstar project, pics with name talent attached still hold the inside track for distribution. Other films at Tribeca with the potential for a wide release include “The Good Doctor,” a psychological thriller starring Orlando Bloom; the Chris Evans-toplined legal drama “Puncture”; quirky family comedy “Jesus Henry Christ” starring Toni Collette; Tony Kaye’s star-filled drama “Detachment” ;and the rockumentaries “Talihina Sky: The Story of Kings of Leon” (shown as a work in progress); and “God Bless Ozzy Osbourne.”

There are also hopes that big-name talent might swoop in to lend a smaller film (like the dark comedy “Rid of Me”) an exec producer credit and, in turn, a distributor.