Transit advocates and several politicians are pushing for a suspension of fares throughout the entire MBTA system during a 30-day Orange Line shutdown that begins Friday and has transportation brass advising people to avoid the Boston region.

Stacy Thompson, Livable Streets executive director, said the group is estimating that eliminating fares for a month would cost approximately $35 million, which is $2 million less than the T is paying for replacement shuttle bus service during the Orange and partial Green Line closure

“To make the entire system free, including the commuter rail, we’re talking about a minimal expense in the grand scheme of things,” Thompson said. “I understand not everyone is on board for free fares all the time. I would say this is a suspension of fares to alleviate stress during the crisis.”

To get that cost projection, Thompson said the group looked at the MBTA’s budget projection overview, which anticipates $474 million in fare revenue this fiscal year. That number was divided by 12, and reduced by the group’s projected $5 million in fare revenue loss between the two line closures.

MBTA spokesperson Joe Pesaturo said the estimated fare revenue loss for the Orange Line closure is between $2.5-$3.5 million, “with actual fare revenue loss being highly dependent on how riders respond to the closure and use alternative service options.”

The push for free fares was announced in a Tuesday press release, which has the support of U.S. Sen. Ed Markey, U.S. Rep. Ayanna Pressley, Boston Mayor Michelle Wu, Somerville Mayor Katjana Ballantyne, state Sen. Pat Jehlen, state Rep. Christine Barber, and a number of transit advocacy groups.

“The Legislature approved $266 million in this year’s state budget to address the safety repairs recommended by the FTA, so there is funding available to support this initiative,” said Rick Dimino, A Better City president and CEO.

The MBTA and Gov. Charlie Baker both remain resistant to system-wide free fares.

“With ridership and revenue still well below pre-pandemic levels, the T’s carefully balanced budget is not prepared to absorb another significant revenue loss,” Pesaturo said. “The bus shuttles will be free, and three of the busiest regularly scheduled bus routes that feed into the Orange Line are also free (through) the ongoing pilot program.

“Additionally, customers can board any commuter rail train in Zones 1, 1A and 2 by simply showing a CharlieCard or CharlieTicket to a conductor.”

However, Thompson said that won’t help many riders impacted by the closure, who may not be familiar with the different commuter rail zones, lack a CharlieCard, or have to pay a full fare for a bus route that connects to the Orange Line.

“Full fare suspension on all modes will help convince more people to take the train, bus, or ferry instead of their car and will reduce congestion both for Orange Line shuttles and for those who have no choice but to drive,” added TransitMatters Program Manager Matthew Petersen.