Montag has made a career out of altering her appearance and then talking about it.
"We were immature and we got caught up," Pratt tells In Touch. "Every time we'd go out to eat, we'd order $4,000 bottles of wine. Heidi was going to the mall and dropping $20,000 to $30,000 a day. We thought we were Jay Z and Beyonce."
In 2011, the couple came close to filing for bankruptcy after Montag spent $30,000 on plastic surgery the year prior.
Their financial woes will be outlined in the upcoming E! special "After Shock: Heidi & Spencer," which premieres Monday, Dec. 9.
Montag tells In Touch she feels "like a different person" with her more frugal spending habits now that the paychecks have stopped coming in. Looking back on "The Hills," she tells the magazine that the show "took a toll on my soul. I'm thankful not to have fake fights anymore!"