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It's time to start chucking some cash into your Mars vacation fund. SpaceX's interplanetary Starship hasn't even left Earth yet, but Elon Musk is already speculating about the price of a ticket to Mars.

In a tweet on Sunday, Musk said he's confident that moving to Mars will one day cost less than $500,000 (£390,000, AU$710,00), though that price tag is "very dependent on volume."

Very dependent on volume, but I’m confident moving to Mars (return ticket is free) will one day cost less than $500k & maybe even below $100k. Low enough that most people in advanced economies could sell their home on Earth & move to Mars if they want. — Elon Musk (@elonmusk) February 11, 2019

Musk thinks the ticket price could eventually dip below $100,000, cheap enough that "most people in advanced economies could sell their home on Earth and move to Mars if they want."

A half-million bucks sounds like a lot of money, but compare that to the over $200,000 price to experience weightlessness on a Virgin Galactic flight or $9.5 million for a vacation on a proposed luxury space station.

One of the most important tidbits in Musk's tweet is that the return ticket will be free. If you move to Mars and decide you don't like the potatoes, you can head on back to Earth.

SpaceX's stainless steel Starship is under development. The company built a "hopper" prototype to test takeoffs and landings and is also testing the Raptor rocket engine that will power it.

Prior to taking a shot at Mars, SpaceX plans to send Starship around the moon in 2023 with tourists on board.

Musk himself has estimated his chances of moving to Mars at 70 percent. He's been flirting with a Mars account on Twitter, so it's no surprise he might want to take his cosmic crush to the next level.