Elon Musk says he is "confident" moving to Mars will "one day" cost less than $500,000 and "maybe even" cost below $100,000.

While the final cost is "very dependent on [the] volume" of travelers, Musk said the cost of moving to Mars will be "low enough that most people in advanced economies could sell their home on Earth [and] move to Mars if they want." (The median home price in the U.S. is $223,900, according to Zillow.)

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.

The comment was part of a Twitter thread announcing the Raptor engine (the engine which will power the rocket's travels to Mars) has achieved the "power level needed for Starship and Super Heavy."

Raptor just achieved power level needed for Starship & Super Heavy

The Starship is the rocket (formerly called the BFR rocket) that SpaceX is building to go to Mars. The Raptor is the rocket engine that SpaceX is making to power the Starship. The Starship will have seven Raptor engines and the booster that launches the rocketship, called Super Heavy, will have 31 Raptor engines, a SpaceX spokesperson tells CNBC Make It.

The "aspirational goal" for SpaceX is to send the first rocket to Mars (with cargo only) in 2022, according to SpaceX's website. The second mission, which will take more cargo and crew, is aiming to go in 2024.

"The objectives for the first mission will be to confirm water resources, identify hazards, and put in place initial power, mining, and life support infrastructure," SpaceX website says. The second mission has "primary objectives of building a propellant depot and preparing for future crew flights. The ships from these initial missions will also serve as the beginnings of the first Mars base, from which we can build a thriving city and eventually a self-sustaining civilization on Mars."

In an article published in academic journal New Space in 2017, Musk also compared the price of trip to Mars to buying a house. At the time, he estimated trips to Mars would cost about $140,000 per ton (taking into account transporting things like luggage, food and life support). But he said at the time he believed the cost could potentially drop to below $100,000 a ton.

"It gets to the point where almost anyone, if they saved up and this was their goal, could buy a ticket and move to Mars — and given that Mars would have a labor shortage for a long time, jobs would not be in short supply," he said.

Musk has said there is a 70 percent chance he himself will go to Mars, once SpaceX gets "the price per ticket to maybe around a couple hundred thousand dollars," he told Axios in a November interview.