This is the Congressional Budget Office (CBO) Cost Estimate as ordered reported by the House Committee on the Judiciary on June 26, 2013. From the Summary: "H.R. 1772 would replace the federal government's existing voluntary system for verifying the employment eligibility of individuals in the United States with a mandatory system. Assuming appropriation of the necessary amounts, CBO estimates that implementing H.R. 1772 would cost about $635 million over the 2014-2018 period and a similar amount in the subsequent five-year period. In addition, CBO and staff of the Joint Committee on Taxation (JCT) estimate that enacting the bill would decrease direct spending and increase on-budget revenues but decrease off-budget revenues. (Payroll taxes for Social Security are classified as off-budget revenues.) Summing those budgetary impacts, CBO and JCT estimate that enacting H.R. 1772 would increase budget deficits as measured by the unified federal budget by about $30 billion over the 10-year period."
Congressional Budget Office: http://www.cbo.gov/