BART will spend $227 million on a new headquarters in downtown Oakland, despite last-minute concerns that it’s not a good use of taxpayer money.

The agency’s Board of Directors voted 8-1 Thursday to approve the move to 2150 Webster St., blocks from BART’s current headquarters near Lake Merritt.

Real estate manager Sean Brooks touted the move as a long-term cost-savings for BART, anticipating the transit agency’s rent would rise more than 60% at the Kaiser complex at 300 Lakeside Drive after its lease expires in 2021. Staying put would also require BART to consolidate its operations in the lower 10 floors of the Lakeside building, instead of the 14 floors it uses today.

The new building would secure a home for BART in the coming decades, provide easy access for employees and members of the public and burnish the “overall image” of the transit system.

But the price — $142 million, plus $85 million for tenant improvements — alarmed Board Director Debora Allen. She said BART had not explored all of its options, including negotiating a new five-year lease in the existing building, constructing another office complex on one of its properties in West Oakland or near Lake Merritt, or pursuing office space somewhere else in the Bay Area, where real estate is cheaper.

“Brand new Class A space in a very hot market in downtown Oakland — I’m not sure if that’s an option a public agency should be considering,” Allen said at the board meeting, reminding her colleagues that BART is 70% funded by taxpayers. She was the lone dissenting vote against the purchase.

The executive director of Contra Costa Transportation Authority sent a letter to BART General Manager Bob Powers on Tuesday, urging him to scout locations in Contra Costa County, “near one of the 12 BART stations that currently call Contra Costa County home.”

“As SF Bay Area housing costs skyrocket, more and more employees are moving further east, therefore, San Francisco and Oakland are no longer considered the ‘center,’ of our region,” Executive Director Randell Iwasaki wrote in his letter. “Perhaps it’s time public agencies follow suit and consider a less expensive area like Contra Costa County, where our commercial real estate costs less than in Alameda or San Francisco counties.”

He failed to persuade BART officials who want to keep their home in the center of the rail system.

“It’s important to stay rooted in Oakland,” said Director Janice Li, whose district spreads through San Francisco. She said she would be unable to serve on the board if BART’s headquarters were near the end of the line in Concord or Fremont.

BART also considered leasing another downtown Oakland building at 601 12th St., which would be substantially more expensive, costing $295 million more than the Webster Street site over a 25-year term, Brooks said.

The agency will issue $227 million in sales tax revenue bonds to buy and renovate the new 2150 Webster St. property.

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan