Elon Musk told Miami’s mayor Friday that The Boring Company could dig a two-mile tunnel under the city for as little as $30 million — a fraction of the $1 billion price tag once quoted by local transit officials. Musk also told the Mayor that The Boring Company could complete the job in six months, versus the original four year estimate.

Mayor Francis Suarez shared these details about his “wonderful call” with Musk in a video posted to Twitter. “He’s focused on trying to deliver a project that will have the maximum utility for our residents for the least amount of money,” Suarez said. “The order of magnitude in terms of savings is significant.”

Musk first tweeted about wanting to tunnel under Miami on January 18th. “Cars & trucks stuck in traffic generate megatons of toxic gases & particulate, but @boringcompany road tunnels under Miami would solve traffic & be an example to the world,” he wrote. Musk said in the tweet that he had already spoken to Florida Governor Ron DeSantis about the idea. “If Governor & Mayor want this done, we will do it.”

Suarez said Friday that he will speak to DeSantis and the mayor of Miami-Dade county. “I think we have a unique opportunity to create a signature project not just for Miami, but for the world,” he said.

Tunneling under Miami is not easy because the city is built on limestone, which is spongey. That hurdle is one reason for the sky-high price tag quoted in 2018. It also helped drive up the price of a tunnel under the Port of Miami, which was less than a mile but still cost around $700 million.

The Miami Herald reported Friday that the limestone bedrock and the impact of rising sea levels were among the talking points for the call, though it’s unclear to what extent these items were discussed. Musk has previously talked about digging tunnels as deep underground as skyscrapers are tall.

Musk started The Boring Company in 2016, and has started a handful of projects around the country in the years since. The purpose and scope of the tunnels has changed a bit over that time. These days, the company is trying to make a transportation service that uses Teslas traveling through the tunnels. The first commercial service is nearing completion underneath the Las Vegas Convention Center, though The Boring Company recently announced a massive city-wide expansion that would service the Strip and the airport. The company is also in negotiations for a tunnel in San Bernardino County, California.

Other attempts have not gone so well, like a failed project in Chicago and a canceled tunnel in West Los Angeles.