Estimating that the costs could reach $5 million with appeals, Republican state Sen. Jeff Denham said he will introduce a bill when the Legislature convenes next month to get the state to cover 100 percent of the bills.
Authorities in Stanislaus County and Modesto, where Scott and Laci Peterson lived, have spent about $2.1 million so far. San Mateo County, where the trial was held after the defense argued that Peterson had been demonized in his hometown, has spent $320,000.
Peterson, 32, was convicted last week of murder. The jury will return next week to decide whether he should get the death penalty.
On Wednesday, defense lawyer Mark Geragos filed a motion in San Mateo County Superior Court for a new jury in a different county to decide whether the former fertilizer salesman gets the death penalty or life in prison without parole for killing his wife and the fetus she carried.
The motion marks the second time Geragos has sought to have two juries seated for the trial, one for the guilt phase and one to determine the penalty.
The cost estimates came amid a fight between the two counties where the nearly 2-year-old case has taken place.
The original deal stipulated that Stanislaus County would reimburse San Mateo County for the trial costs. But San Mateo County is frustrated with the slow pace of reimbursement, and officials there said Thursday they want a court order compelling Stanislaus to pay up.
In a letter, San Mateo County Supervisor Mark Church said it is "imperative" that the county be reimbursed to avoid cuts in county services.
Stanislaus County Auditor-Controller Larry Haugh said the county will pay, but added, "Things are tight."
San Mateo County's bill included more than $320,000 for jailing Peterson through most of 2004, using a courtroom for five months and keeping jurors in $135-a-night hotel rooms. The county seat of Redwood City also claims that controlling traffic, media and crowds outside the courthouse have cost city taxpayers more than $70,000.
Laci Peterson vanished just before Christmas 2002; her remains and that of the male fetus turned up on the shore of San Francisco Bay four months later.