And the tab seems to grow by the day.
"The hard part is prices have changed and gone up. There are things that can come up that are just completely unforeseen," Wallenda said by phone from Branson, Mo., where he was juggling walk preparations with production of a stage show with his high-flying family. Wallenda, who lives in Sarasota, Fla., is a seventh-generation member of the Flying Wallendas.
There hasn't been much time to line up sponsors the date of the walk was settled only about six weeks ago so Wallenda is asking the public for donations.
His video on the fundraising website Indiegogo had, by mid-day Tuesday, raised more than $15,300 toward a $50,000 goal.
Wallenda plans to walk 1,800 feet across the falls at 200 feet above the gorge bottom. If successful, he will be the first to cross over the brink of the famous falls. Others have crossed over the gorge downstream but not for more than 100 years.
"We need stuff like this," Wallenda says on the video. "We need things to encourage people that the impossible is actually possible."
Wallenda has agreed to pay Canadian authorities $105,000 for things like extra security, crowd control, fencing and portable toilets for the estimated 100,000 spectators. He also must supply a $50,000 letter of credit, which would be used only in the event of a water rescue, said Niagara Parks Commission Chairwoman Janice Thomson. Such a rescue is more unlikely now that ABC is requiring Wallenda to be tethered to the wire.
To U.S. authorities, Wallenda paid a $5,000 permit fee and will reimburse New York state $150,000 for state police and transportation services, the state Office of Parks, Recreation and Historic Preservation said. He also was asked for a $25,000 deposit to ensure he restores the Niagara Falls park to its original condition.
The 7-ton cable he'll walk on will be anchored deep into bedrock a few hundred feet back from both shores and will be held by steel support structures.
While the walk initially was expected to cost about $1 million, unexpected, big-ticket expenses have driven up costs, Wallenda said, including the need to fabricate two high wires instead of one. Initially, Wallenda intended to practice on the same cable he'll perform on but he couldn't find a space in Niagara Falls large enough to string it. That meant crimping the practice cable to shorten it and ordering a new one for the walk.
"So that budget almost doubled," he said.
Then last week, the Niagara Falls, Ontario, helicopter company he'd asked to fly a guide wire across the gorge, so that the actual cable can be pulled across, discovered it didn't have the necessary Federal Aviation Administration permits for such an operation and Wallenda had to scramble to find a replacement company, in Pennsylvania.
"You have to get a helicopter company last minute, that hurts," Wallenda said. "There are things like that that come up that are completely unforeseen ... $50,000, $100,000. These are big, big line items."
Although the walk will be broadcast live on ABC, Wallenda said legal liability considerations prevent the network from specifically funding his preparations, materials and all the others costs that go his act.
He's hoping thank-you gifts for donors will push the Indiegogo numbers up.
For $5, donors get a picture from the walk, for $10, an autographed poster. As of mid-day Tuesday, one person had pledged $5,000 for access to a VIP viewing area and dinner with Wallenda. There were no immediate takers for a private Wallenda-taught backyard wirewalking lesson, dinner and VIP viewing, for $10,000.
Wallendas have rich history, not without tragedy
When Nik Wallenda sets out for his tightrope walk over Niagara Falls late Friday, he'll be adding another chapter to his family's storied daredevil history which dates back more than two centuries. Wallenda has said he is disappointed he is being made to wear a tether by the event's sponsor, ABC, since his family has performed over the years without such safety precautions.
Here's a look at the first family of funambulists, along with some of their notable feats and tragedies:
The Wallendas trace their fearless roots to 1780 Austria-Hungary, when ancestors traveled as a band of acrobats, aerialists, jugglers, animal trainers and trapeze artists.
John Ringling of the Ringling Bros. and Barnum & Bailey Circus recruited the Wallendas after seeing them perform in Cuba. In 1928, the family gave its inaugural performance at Madison Square Garden earned a 15-minute standing ovation from an astounded audience, who marveled at them performing without a safety net.
The signature performance of the group that came to be known in the 1940s as "The Flying Wallendas" was the seven-person chair pyramid: Two pairs of performers walk the wire, each supporting another aerialist on a pole. Those two aerialists, in turn, carry a pole upon which the seventh member of the troupe balances in a chair.
The chair pyramid went terribly wrong in 1962 when a misstep at the State Fair Coliseum in Detroit sent two men to their deaths and paralyzed a third performer.
In 1944, the Wallendas were performing at a Hartford, Conn., circus when a fire broke out. All the Wallendas slid down ropes to safety but 168 people died.
The following year, Rietta Wallenda, sister-in-law of family patriarch Karl Wallenda, fell to her death in Omaha.
Family patriarch and Nik's great-grandfather Karl Wallenda became a featured performer, doing "sky walks" between buildings and across stadiums including Busch, Veterans, JFK, Three Rivers and the Astrodome.
Karl Wallenda successfully crossed Tallulah Gorge on a tightrope on July 18, 1970.
In 1978, Karl Wallenda fell to his death while attempting to walk a cable strung between two hotel towers in San Juan, Puerto Rico.
Angel Wallenda, who married into the family at age 17, performed with an artificial limb on the high-wire in 1990 after being stricken with cancer and having her right leg amputated below the knee. She died at age 28 in 1996.
Since first stepping on a wire when he was 2, Nik Wallenda has earned six Guinness records, the latest in October 2008. That's when, 20 stories over the streets of Newark, N.J., he traveled the longest distance and the greatest height by bicycle on a wire, riding 150 feet.
In 2011, Nik and his mother Delilah honored his late great-grandfather by walking Karl's last route at the same time, a feat that included Nik stepping over his mother in the middle of the wire.
Fourteen family members perform today in various troupes.