Mark Cuban shares the book that helped him earn his first $1 million

Now a judge on ABC's "Shark Tank" and owner of the Dallas Mavericks, Mark Cuban became a billionaire back in 1998 when he and Todd Wagner took their online audio streaming company, Broadcast.com, public.

But Cuban had been a millionaire long before he entered the three-comma club. And he credits the drive to earn his first million to a book he read when he was just starting out: "Cashing in on the American Dream: How to Retire at 35" by Paul Terhorst, as he told Money in a recent interview.

The book centers on the idea of focusing on your priorities and living well below your means. It encourages readers to downsize their houses, cars and other expenses, and spend time developing their passions and finding meaning in their lives beyond work.

"I did things like having five roommates and living off of macaroni and cheese, and I was very, very frugal," Cuban told Money.

Even as the entrepreneur's career began to take off, the lessons he learned in "How to Retire by 35" inspired him to stick to his frugal habits.

"I didn't have a car that cost more than $200 until I was 25, I think," he says. "It was crazy."

Cuban doesn't regret his beat-up rides and macaroni dinners. At the time, his only focus was on saving for the future and building up a sizable nest egg that would eventually allow him to retire comfortably.

"It wasn't like I thought, 'Okay, I'm going to be super-rich,'" he says. "I valued time more than anything. I wanted enough money to be able to travel, have fun and party like a rock star, but still live like a student. That was my motivation."

That's not to say Cuban is unwilling to splurge: If it saves him time, it's worth it. In the late '90s, he bought his first private jet, a purchase he still credits as the smartest thing he ever spent money on.

"It is obviously brutally expensive, but time is the one asset we simply don't own. It saves me hours and hours," he wrote in a column for Men's Fitness.

Cuban's not the only billionaire willing to pay for the convenience of time. John Paul DeJoria, co-founder of Paul Mitchell hair products and Patron Tequila, owns three private jets himself .

"For him, time is a precious commodity and he'll do what he must to preserve it, even if it means spending millions of dollars on his own airplanes," writes Farnoosh Torabi , who shadowed DeJoria on the CNBC show "Follow the Leader." "His jets allow him to conduct meetings on the go and around the country without wasting hours at the airport."

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