Congressional Budget Office Cost Estimate: S. 148: A Bill to Provide for the Secretary of Homeland Security to be Included in the Line of Presidential Succession [open pdf - 8KB]
"S.148 would amend the Presidential Succession Act of 1947 to include the Secretary of Homeland Security. The bill would place the Secretary of Homeland Security eighth in line to succeed the President directly following the Attorney General. CBO estimates that implementing S. 148 would have no cost and would not affect direct spending or revenues. This legislation contains no intergovernmental or private-sector mandates as defined in the Unfunded Mandates Reform Act and would impose no costs on state, local, or tribal governments."
Congressional Budget Office: http://cbo.gov