Trading of Tesla stock has now been halted following this news & Elon's tweets.
https://www.cnbc.com/2018/08/07/tesla-stock-jumps-on-musks-t...
https://www.cnbc.com/2018/08/07/tesla-stock-jumps-on-musks-t...
Other buyouts of such scale involved companies with huge cash flows/profits - think RJR Nabisco, Hilton, TXU (big US utility).
Tesla of course is a very different animal. Hard to imagine any kind of conventional financing working for this type of deal.
Beyond the Saudis maybe some other SWF or deep pocketed individual investors?