In one of Sundance’s surprise success stories, Fox Searchlight nabbed worldwide rights to Borderline Films principal Sean Durkin’s writing-directing debut, “Martha Marcy May Marlene,” with Durkin going on to win the fest’s directing award. The quick sale for a reported $1.6 million, of this low-budget tale of a cult survivor (produced with This Is That Prods.) may have been unexpected, but not surprising considering Borderline Films’ track record.The Brooklyn-based feature, commercial and musicvideo production outfit formed in 2003 at NYU’s Tisch School of the Arts, where Manhattan high school acquaintances Josh Mond and Antonio Campos met Durkin. Borderline’s (and Campos’) first feature, the IFC Films pickup “Afterschool,” nabbed top Gotham and Indie Spirit nominations for its moody, experimental take on a high school tragedy. The three principals named Borderline for the divide between commercial and arthouse fare they hope to blur, Durkin says, and it also aptly describes how their outfit straddles a production company and film collective. “We all direct and produce, share everything equally and support each other,” says Durkin. They live a stone’s throw away from each other in Williamsburg, where they mainly work from their apartments. “It’s very organic when a short-form job comes in,” Mond adds. “If Sean’s writing, then that’s his focus, and Tony and I will figure out who’ll do the job as director and producer.” The collaboration extends to their features — all were heavily involved in the writing and editing process on Borderline’s second feature, writer-director Alistair Banks Griffin’s drama “Two Gates of Sleep,” which is playing the fest circuit. “The only time I feel really alive or happy is when I’m on set, and the only way I get through other periods is being so creatively involved on all these other projects,” Campos says. “I think that’s what keeps us all going — we never stop.” Their first effort was not as auspicious: Financing fell through for what would’ve been Jonah Hill’s first feature role in 2004, a high-school laffer called “Laid,” but it inspired the trio to start at a less-expensive level: video shorts. The new approach paid off when their first, the $1,000 drama “Buy It Now” won the top Cinefondation prize at the 2005 Cannes Film Festival. Borderline still keeps its budgets well under seven figures with private equity and, like many production houses, does commercials and videos to pay the bills. “Hopefully we can pay our crew a little more money on those than we can pay on the features,” says Campos, adding that several returning crew members and actors like Brady Corbet, who appears in “Martha Marcy” and “Two Gates of Sleep,” are “really a family.” Up next: In addition to a TV pilot pitch they’re jointly developing, Campos is editing his improvised romantic drama “Simon Killer,” and working on a second draft of “Momma,” which chronicles 30 years in the relationship between a young filmmaker and his mother. Mond, who helmed the acclaimed Mayday Parade video “Kids in Love,” is negotiating for rights to a “surreal, paranoia-filled” graphic novel to adapt for his feature debut. The three are starting conversations with investors for an overhead deal, but until that happens, their new Searchlight money will come in very handy. “My phone literally shut off about an hour into the (‘Martha’) negotiations because I couldn’t pay my bill this month,” Campos recalls with a laugh.