In the wake of Elon Musk's announcement about a private trip to the moon, people wonder exactly how much it costs to qualify as a moon tourist. Musk has mentioned that the two mystery space tourists put down a “significant deposit” with SpaceX. He wouldn't say about how much money the secret passengers are shelling out for their Moon voyage, but as it turns out, it’s incredibly difficult to guess the costs of human spaceflight.

Unsurprisingly, a lot goes into launching someone into space, especially to the moon. First, there are the obvious costs such as the spacecraft, the rocket, and the fuel. Second, there are the less obvious cost such as the money to be used in the years and equipment needed to train the astronauts.

According to the Verge, a trip to the moon also needs building and maintaining the launchpad, paying the people on the ground in mission control, having rescue plans and personnel ready to get the astronauts or space tourists to safety if there’s an emergency. “It’s always a more complex answer,” Daniel Huot, a spokesperson for NASA, explains. He adds that sending people to space is an expensive matter.

However, here’s what we do know from what Musk have said about the space price. Although he wouldn’t specify it, he did say that the around-the-Moon mission could cost roughly a bit more or the same when sending a whole crew to the International Space Station. Asked for clarification, SpaceX declined to answer in an emailed request, the NBC News reports.

Right now, the closest estimate we can get for a trip to the moon is roughly the same price NASA is paying the Russian space agency Roscosmos. That's about $81 million, which is a bit more expensive than the latest five seats NASA bought in bulk at about $74.7 million per seat. That's what the two mystery soon-to-be moon tourists must be paying for their space trip.