Congressional Budget Office Cost Estimate: S. 1884: Reporting Efficiently to Proper Officials in Response to Terrorism Act of 2017 [open pdf - 88KB]
"S. 1884 would require the primary government agency investigating an act of terrorism that occurs in the United States to report to the Congress not later than one year after completing the investigation. That agency would have to collaborate with the Department of Homeland Security and other federal bodies as appropriate. The report would identify weaknesses in national security and recommend additional measures to improve homeland security and prevent terrorist acts. In recent years there have been few incidents of domestic terrorism, so CBO expects that implementing S. 1884 would require a small number of reports each year, on average. Based on the cost of similar activities, CBO estimates that providing the reports would cost less than $500,000 annually; such spending would be subject to the availability of appropriated funds."
Congressional Budget Office: https://www.cbo.gov/