The Oakland A’s have come to a tentative agreement to buy Alameda County’s half ownership of the 155 acre Oakland-Alameda County Coliseum site.

The price: $85 million.

“It’s way to keep the A’s in the East Bay and at the same time finally get us out of the sports business,” said Supervisor Scott Haggerty, who also sits on the Coliseum Authority board.

A’s President Dave Kaval said the team’s first choice for building a new ballpark is still at the Port of Oakland’s Howard Terminal.

“We are still 100% committed to the waterfront ballpark at Jack London Square,” Kaval said, “but this other project in East Oakland is not only good for the city. It’s also good for the A’s.”

The A’s are looking to keep Oracle Arena and turn the Coliseum into a chopped-down “roman ruin-like” multisports facility. There would also be parks, housing and a technology campus.

“So we could have a tech partner in this,” Kaval said.

The county will use the $85 million to pay off its portion of the outstanding bond debt on the Coliseum from the renovations needed to bring the Raiders back from Los Angeles in 1995. Soon, of course, they’re headed to Las Vegas.

Add in other expenses for operating the Coliseum and arena, and the county expects to save roughly $13 million a year, County Administrator Susan Muranishi said.

Oakland Mayor Libby Schaaf had hoped to buy out the county’s share and thus take full control of the site, giving the city leverage in future negotiations with the A’s on developing the site.

The city, however, never came up with a solid offer or the money to swing the deal, although Oakland could still fight it in court.

Schaaf told us that while the sale “could be a creative approach to accelerate development of the Coliseum,” it is “unclear if the county has the right to sell its share of our jointly owned land.”

Not exactly a resounding endorsement.

A vote to begin negotiations on the sale is expected to be taken at the Board of Supervisors meeting Tuesday.

San Francisco Chronicle columnist Phillip Matier appears Sundays and Wednesdays. Matier can be seen on the KPIX-TV morning and evening news. He can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call 415-777-8815, or email pmatier@sfchronicle.com. Twitter: @philmatier