The mayor of Somerville says new estimates that the Green Line extension could cost as much as $1 billion more than initially predicted don't necessarily mean the project will be canceled or even postponed.

“Let’s be clear: the state has a legal obligation to build the Green Line. That’s clear cut, that’s black and white,” Mayor Joseph Curtatone said in an interview, referring to a settlement that requires the state to complete the extension to mitigate the impacts of the Big Dig.

He added: “The state [also] wants to build the Green Line. We have billions of dollars in economic development in Somerville and Cambridge and the region relying on the Green Line expansion.”

Transportation officials revealed Monday that the full cost of building seven new Green Line stations in Cambridge, Somerville and Medford could cost as much as $3 billion, $1 billion more than initially estimated.

"Oh my god. That is a lot of money," said Brad Moeller, who lives in Somerville's Union Square — the site of one the first new Green Line stops scheduled to open in 2018.

A map of the proposed Green Line extension project. (Mass.gov)

Moeller says he wouldn't mind if the entire project was canceled so that his rent stays lower — a sentiment that's not shared by Anne McGuinnes.

"I think it's terrible," McGuinnes said. "They've been promising it for a long time and they've already started significant construction over there."

McGuinnes, who works in Union Square, says she thinks the higher price tag will cause the T to abandon the project. She points to statements from Transportation Secretary Stephanie Pollack, who says all options, including canceling the project, are on the table.