Investing legend Warren Buffett has an estimated net worth of $74 billion, making him the third richest man in the world. But you'd never know it from his lifestyle.

The 86-year-old billionaire still lives in the five-bedroom home in Omaha, Nebraska, that he bought in 1958 for $31,500. And he never spends more than $3.17 on breakfast.

On his five-minute drive to the office, which he's been doing for the past 54 years, Buffett stops by McDonald's and orders one of three items.

"I tell my wife, as I shave in the morning, I say, 'Either $2.61, $2.95 or $3.17.' And she puts that amount in the little cup by me here [in the car]," he explains in HBO's documentary, "Becoming Warren Buffett," which debuted Monday.

Each amount corresponds with a different option at McDonald's.

"When I'm not feeling quite so prosperous, I might go with the $2.61, which is two sausage patties, and then I put them together and pour myself a Coke," he tells director Peter Kunhardt in the documentary.

"$3.17 is a bacon, egg and cheese biscuit, but the market's down this morning, so I'll pass up the $3.17 and go with the $2.95."

Buffett proceeds to order a sausage, egg and cheese and pay using exact change.