Elon Musk has costed an idea from a former Australian Greens MP of a tunnel through NSW's rugged Blue Mountains at "around $750 million with additional costs".

Technology entrepreneur Elon Musk has hinted interest in helping solve Sydney's road congestion, quoting $1 billion on Twitter for a high-speed transit tunnel through Australia's Blue Mountains.

A New South Wales MP has pitched the idea of building a 50-kilometre tunnel to Musk, who quoted "a bargain" to build it, according to tech billionaire Mike Cannon-Brookes.

Former Greens MP Jeremy Buckingham tweeted to Musk, "How much to build a 50km tunnel through the Blue Mountains and open up the west of our State?"

BROOK MITCHELL Australian politician Jeremy Buckingham has proposed tunneling under the Blue Mountains to "open up the west" of New South Wales.

Musk, the founder of the electric car company Tesla and The Boring Company, which is aiming to transform high-speed transportation through tunnels, replied saying it would cost around $750 million with additional costs.

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He didn't specify if he was referring to US dollars, in which case it would make it AUD$1.045 billion or $1.47 billion New Zealand dollars.

@greensjeremy/TWITTER Elon Musk has said it will cost around $1 billion to build a Blue Mountains tunnel after Australian MP Jeremy Buckingham proposed the project via tweet.

"About $15M/km for a two-way high-speed transit, so probably around $750M plus maybe $50M/station," Musk wrote on Twitter.

About $15M/km for a two way high speed transit, so probably around $750M plus maybe $50M/station — Elon Musk (@elonmusk) January 16, 2019 "Thanks, mate. Sounds like a bargain," Buckingham replied to this quote and promised to raise it with NSW State Premier Gladys Berejiklian. Musk's Boring Company is currently testing a two-kilometre tunnel in Los Angeles and plans to construct another in Chicago. Australian tech billionaire Mike Cannon-Brookes, who was tagged in the exchange, agreed the proposal; "sounds like a bargain for Sydney". @elonmusk hope you’re well mate.



Thanks for making my phone go bananas 😂 wondered what was up. Sounds like a bargain for Sydney.



PS Tesla phone support fabulous tonight for tyre pressure issue 👏🏻 Good luck on the Deagon crew launch in Feb! 🚀🙏🏻 https://t.co/8cH2yhf604 — Mike Cannon-Brookes 👨🏼‍💻🧢 (@mcannonbrookes) January 16, 2019 Thanks mate. Sounds like a bargain. Could be a game changer to go under the Blue Mountains with a modern link between Sydney and the west. I’ll raise it with the Premier @GladysB other colleagues, the community, and get back to you. — Jeremy Buckingham 🌏 (@greensjeremy) January 16, 2019

Cannon-Brookes and Musk have history when it comes to making infrastructure deals via Twitter.

Musk's company installed the world's largest lithium battery in South Australia in 2017, after he guaranteed over Twitter it could be done within 100 days of a contract being signed or it would be free, in response to a tweet from Cannon-Brookes.

Cannon-Brookes said after the battery was completed that he has "never been more happy to lose a bet".

Of the tunnel proposal, Buckingham said it "could be a game changer to go under the Blue Mountains with a modern link between Sydney and the west".

He said the proposed tunnel would be accessible by a car lift which would place vehicles on a special platform allowing them to travel at high speeds between stations.

"For the price of rebuilding one stadium, Elon Musk says he can build a transport loop for NSW that would be the envy of the world," Buckingham said.

It's not clear when Musk's boring technology will be ready for a 50km job, nor what fluctuations in price would occur by then.