GOOD MORNING: Here’s how to save $10 million while making a big-budget movie: “The Phantom,” Par’s biggie for summer ’96, was skedded to film interiors on the Sony lot, with jungle exteriors in Hawaii. But I got the economizing explanation Monday from producer (with Bob Evans) Alan Ladd Jr., director Simon Wincer and writer/co-producer Jeffrey Boam on Universal’s giant New York Street, when they were readying sequences of the 1938-set conversion of the classic comic book-to-bigscreen. Over 50 vintage cars, trucks, taxis, etc., of the era and 300 appropriately attired extras were assembled with co-stars Billy Zane and Kristy Swanson. (The studio’s New York streets will be enhanced and backgrounded with complete N.Y. skylines and skyscrapers, thanks to today’s high-tech computers. It will be done by Buena Vista.) When Par found out how much it would cost to shoot interiors at Sony and jungle sequences in Hawaii, a big shift came into play: the sets, already started at Sony, were shipped to WB’s Roadshow Studios outside Brisbane (where Wincer has worked), Hawaii was shifted to Thailand (where Wincer has worked) and the New York Zoo and Central Park became Griffith Park. And since “The Phantom” is a favorite of Hugh Hefner’s, he allowed them to use his Playboy mansion for the first time. Now, says Laddie, the budget’s “in the 40s.” He explains they are further able to do the mammoth pic for this price “because we have no Kevin Costner or Tom Cruise.” But there’s no cutting down on any of the extravagant sets. Production designer Paul Peters showed me renderings of the sets: They are spectacular — on land, underwater and in the air. And they are en route to their faraway filming destinations as we speak. Costume designer Marlene Stewart showed me “The Phantom’s” costume, created in 10 weeks. (“Batman,” they pointed out, had a year’s designer development.) “The Phantom” has a body-hugging suit that glistens in the light, with its moire design inspired by natives’ tattoos. His cowl was designed by Jim Henson’s Creature Shop along with Stewart and it peaks on Zane’s forehead above a black mask that covers his eyes. Billy Z. looks like the comic book character come to life. And his lady love, Kristy Swanson, looks amazingly like the comic book Diana Palmer — Wincer gave me a copy of the original 1936 “Phantom” comic book to prove it. The comic still sells out twice monthly in Australia and other countries, they tell me. Zane is in such good physical shape, Wincer says, his stuntmen doubles cannot have an ounce of fat — it would bulge in the body-hugging “Phantom” suit! Zane says being on the U lot brings back memories of his first film, “Back to the Future” 10 years ago, “when I did my own stunts — and had a much smaller trailer!”… Laddie, who is no stranger to epix — his most recent was “Braveheart”– next returns to an intimate family film: “Very Brady,” the “Brady Bunch” movie sequel. Arlene Sanford directs, starting in January. She and Betty Thomas (who directed the first “Brady” feature) followed one another on the “Dream On” series — both also winning awards … Jeffrey Boam is also working on scripts for “Indiana Jones IV” and “Lethal Weapon 4.” As for “Indie,” he says Steve Spielberg wants the pic to shoot here. Only one week will be on location, probably in Honduras. Russia had first been planned. “And,” added Boam, Harrison Ford will play his own age, “so he can limp and/or wear glasses!”“WELCOME TO PEARL HARBOR,” the sign said outside the breakwater, so Ian Ziering and girlfriend Nikki Schiede, aboard his Wave Runner (y’know, those water motorcycles), zoomed into Pearl at 40 mph, scooted up to the Arizona memorial. “I suddenly realized I was on hallowed ground,” the youngstar of “Beverly Hills, 90210″ told me. They headed to a landing — where Navy Shore Patrol and police were waiting for ‘em. After lengthy interrogation (Ziering wasn’t recognized), they were released, warned, told how to properly return to the Ihilani hotel, where they had earlier been part of Marjoe Gortner’s celeb tourney. He’s now back here on terra firma and the Spelling series. He says he loves the show, but is planning his feature banner with Cyd Levin, Dabble Inn Corp. “We have funding for $ 3 million-$ 5 million pix,” he says. AFTER A LONG, UNOFFICIAL separation, Frank Langella and wife Ruth are ending their 17-year marriage. They have two children. She’s filing for divorce … Walt Disney’s grandchildren, Joanne Miller Runeare and Walter Disney Miller, will be on hand Thursday when Walt’s never-before-seen-by-the-public collection of miniatures goes on display (through April) at Carole and Barry Kaye’s Museum of Miniatures. Carole told me she tracked down the miniatures (Walt’s first love) in a storage house … Gilda’s Club Corporate Vision Awards are presented Monday at the Pierre in N.Y. Gene Wilder, Joanna Bull (Radner’s therapist during her cancer fight) and Jonathan Tisch are honorary chairs. People mag’s Ann Moore and Vanity Fair alumnus Peter J. Vilardi are recipients.