Sonoma-Marin Area Rail Transit officials laid their cards on the table and gave their best estimate of the final cost to complete the first segment of commuter rail line by 2016. The price tag: $427.9 million.

The cost of the line has been a bit of a moving target as the length of the initial segment has grown. The full project, as approved by voters in 2008, was a 70-mile line from Cloverdale to Larkspur. But when the economy tanked and SMART officials realized they didn’t have the sales tax revenue to build the whole thing at once, they decided to do it in phases.

The first phase was originally going to be from downtown Santa Rosa to the Marin Civic Center. In 2011, the best estimated cost was $403 million. As the economy improved and SMART’s sales tax revenue increased as well as its ability to attract grant funds, officials have added new pieces to the initial operating segment. It is now nine miles longer, from Airport Boulevard to downtown San Rafael, and $25 million more expensive.

SMART’s ultimate goal, to get to Cloverdale and Larkspur, is still about $230 million short. Farhad Mansourian, SMART general manager, has said he is continuing to look for funding to complete the project.