Harvard owns 358 acres in Allston, where it plans to redevelop land into a new science and innovation cluster.

Massachusetts has pursued realignment plans for a stretch of the Massachusetts Turnpike in Boston’s Allston neighborhood for years, but debates over the scale, transit mitigation and who picks up the tab have pushed construction back well past its intended 2016 start date. State officials revealed Monday the project will move forward sometime in 2020 but with a new price tag reminiscent of that pricey downtown tunnel.

The state intends to push forward construction and environmental plans for changes to the Allston Interchange by the end of November, according to Transportation Secretary Stephanie Pollack. While the project was estimated to cost $260M when it was announced in 2013, the new price tag ranges from $983M to $1.2B, the Boston Globe reports. The final price will be determined by the design direction of the overall project.

The state will replace an aging, raised portion of the Pike with a straightened highway, instead of the looping path it takes through shuttered Beacon Park rail yards. A new commuter rail station would be constructed along with a grid pattern of streets and potentially more parkland along the Charles River, depending on which design option is pursued.

A $1B option with a new elevated highway and a more inland Soldiers Field Road would deliver the added green space. The pricey, $1.2B option entails rebuilding the turnpike at street level while decking over the highway with train tracks. The most economical option would see both road and rails at ground level.

The sizable project will not be fully funded by just toll revenue, which likely cannot foot the bill for the new rail station. Pollack indicated the state could look for outside financing, and some say Harvard should help pay since it is looking to develop much of the land opened up by the project. MBTA board member Brian Lang said the university should help out, since its real estate ambition would benefit from a new turnpike design.

Harvard indicated to the Globe it had already made “significant contributions” to the project thus far by removing infrastructure from the train yards, providing some of its Allston property for the interchange and committing funds for the new commuter rail station.