Adam Jonas, an analyst at Morgan Stanley, values Spacex at about $46 billion, which is on par with Tesla ($60 billion). His range is pretty wide, though, and spans between $5 billion and $120 billion.
Most of the value of SpaceX, in Jonas' view, would come from a satellite-based broadband business. Jonas sees SpaceX launching lots of satellites into space that would blanket the globe in wireless, high-speed internet. He said that satellite broadband could represent as much as 50% of the total value of space.
Spacex in the testing phase now but hopes to begin launching its first satellites in 2019 and its global network in 2024.
If Spacex's satellite-internet business fails then Spacex could be valued at a smaller $5 billion. Jonas said that if both businesses do better than expected, Spacex could be worth as much as $120.6 billion.
Elon has 33.6 million shares of Tesla (about 19% of the company) worth $12 billion.
If Spacex were worth $46 billion (Elon owns 54% of Spacex) then Elon part would be worth $25 billion.