Customers who pay above €7 are entited to download two more albums at the same price per unit.
The 59-year-old soprano's contract with EMI ended in 2004. Rock band Radiohead, whose recording contract with EMI expired the same year, also issued a pay-what-you-wish album last month.
Released October 10, In Rainbows sold 1.2 million copies within 24 hours, Gigwise reported.
"[The average price paid was] probably pretty close" to Ô£4 (currently $8), Bryce Edge of Courtyard Management, the firm that manages the band, told Billboard.
"What Radiohead did with their album was a genius idea," rapper Jay Z told The Guardian of London. "I'm gonna pay $50 for it."
According to Earthtimes.org, a recent study found nearly 60 percent downloaded the album for free.