Paypal. Article from 2017 estimates $10m or higher (https://qz.com/1026167/elon-musk-just-bought-x-com-the-domain-he-once-owned-from-paypal https://qz.com/10261

Paypal. Article from 2017 estimates $10m or higher (https://qz.com/1026167/elon-musk-just-bought-x-com-the-domain-he-once-owned-from-paypal https://qz.com/1026167/elon-musk-just-bought-x-com-the-domai...) but nobody knows