A Kentucky state commission says that taxpayers there would pay $89 million a year if police were to enforce immigration laws.
The findings are fueling additional objections from critics of a proposal that is halfway through the legislative process.
Staffers in the Kentucky Legislative Research Commission posted the cost estimate.
The legislation would give local and state police agencies broad authority under federal law to check the immigration status of people they stop.
State Sen. John Schickel, R-Union, warned that Kentucky may face an even higher cost if it does nothing while other states pass laws that end up forcing unauthorized immigrants to move.
"If we do nothing, we risk the danger of becoming a sanctuary state for illegal immigrants," he told the House Local Government Committee.
The latest cost estimate is more fodder for critics that say the bill is even tougher than a similar Arizona immigration law that has drawn boycotts and legal challenges.
The Kentucky proposal cleared the Senate on a 24-14 vote last month. Supporters argued that unauthorized immigrants, estimated at between 30,000 and 50,000 in Kentucky, sap government services, and using local and state authorities to enforce federal laws could save the state government's social programs some $50 million.
The bill was among the top priorities of Republicans who run the Senate.
"Does Kentucky want to be a sanctuary for illegals?" said Sen. Tom Jensen, R-London, last month. "What this bill really does is it sends a message ... that we do not tolerate people coming into this country illegally. They should come into this country legally. My grandparents did."
The measure would allow Kentucky law enforcement officers to determine the immigration status of someone who is stopped for another reason, such as a traffic offense, and who is suspected of being an unauthorized immigrant.
The proposal also would allow police to arrest unauthorized immigrants on trespassing charges for setting foot in Kentucky.
This is based on a story by The Associated Press.