THE MBTA CHOSE a joint venture led by a Dallas-area contractor that said it would build the long-delayed seven-stop Green Line extension into Somerville and Medford for hundreds of millions less than officials estimated.

The winning bid by GLX Constructors, a group of four construction and engineering firms led by Fluor of Irving, Texas, was $1.08 billion, including $127.5 million in contingency funds for unexpected costs. The bid was about $236.9 million below the T’s hard-ceiling estimate of $1.32 billion and about $100 million below the only other qualified bidder.

“We’ll build a railroad, that’s what we do,” said Max Jordan, executive director of the Green Line project for Fluor, when asked his reaction after the bids were unsealed. “This is right in our wheelhouse.”

The total cost for the project was set at $2.3 billion, with the federal government contributing about $1 billion and the state putting up $1.3 billion, with smaller contributions from Cambridge and Somerville.

Joseph Aiello, chairman of the T’s Fiscal and Management Control Board, which is slated to discuss and vote on approving the contract on Monday, said he was “delighted with the outcome,” especially in light of the cost overruns in the original contract. Those overruns forced officials to put the brakes on the project when the price estimate hit $3 billion, far above the initial $1.9 billion estimate.

“This whole process was an incredible tribute to the staff to be able to rebound from the problems a few years ago,” said Aiello, who was in the audience watching the bid announcement.

GLX won on a points basis over Green Line Partners, a joint venture led by The Lane Construction Corporation of Connecticut, which submitted a bid of $1.18 billion, including the contingency fund. A third company pulled out earlier in the year when its cost estimates were higher than the T’s maximum allowable price.

John Dalton, the MBTA’s project manager for the extension, laid out the criteria for selection before the bids were unsealed. Dalton said the decision would be “best value determination,” based on a scoring scale that included not just the price but technical solutions, key personnel and experience, and civil rights approaches that include using women, minorities, and veteran subcontractors and employees.

Bidders also received credit for putting up to six options back into the contract that were jettisoned when the initial contract was abandoned. Some of those options included canopies for station stops, an art program, elevators at some stations, and walking paths.

“This is not just the price but also the quality and some of the contingents and options built in,” Dalton said.  “This is not a math problem.”

The project, which was part of the mitigation agreement when the Big Dig was built, will create seven new stops and lay down new tracks between Lechmere Station in Cambridge and Tufts University as well as purchase new Green Line cars. The T has also floated the idea of extending it further into Medford, though that proposal would not be part of this project.

The project was bid and will be built under a new approach, where the contractor does both the design and build phases, that locks in the price and makes the contractor responsible for any overruns except for design changes ordered by the MBTA. Officials said the old approach, which allowed price flexibility as the process moved along, contributed to the spiraling price and the state needed to come up with a new process to maintain cost certainty.

“It’s a hard bid design-build number,” said Aiello. “In my mind, [the old approach] was an inappropriate contractual mechanism to be used for this kind of project.”

Aiello said he was pleased the final bids came in significantly under estimate, saying the debt-ridden agency can ill-afford to throw money out the window.

“Every dollar the T has available to it is a precious dollar,” he said.