Blackstone has agreed to buy majority stake in Spanx, valuing the shapewear maker at $1.2 billion. Sara Blakely had founded the US-based company with $5,000 of her personal savings in 2000 and has bootstrapped it for 21 years. "This is a really important moment in time for female entrepreneurs," 50-year-old Blakely, who became a billionaire once again, said.