Reducing DHS Acquisition Cost Growth Act (Sec. 2) This bill amends the Homeland Security Act of 2002 to require the program manager of a major acquisition program (a Department of Homeland Security [DHS] acquisition program estimated to require an eventual total expenditure of at least $300 million over its life cycle cost) to notify the program's Component Acquisition Executive (CAE) (the senior acquisition official within a DHS component designated to lead a process and staff to provide acquisition and program management oversight, policy, and guidance to ensure that statutory, regulatory, and higher level policy requirements are fulfilled), the head of the component concerned, the Executive Director of the Program Accountability and Risk Management division, the Under Secretary for Management, and the Deputy Secretary of DHS within 30 days after any breach in such program is identified. If such a breach results in a cost overrun greater than 15%, a schedule delay greater than 180 days, or a failure to meet any performance thresholds from the cost, schedule, or performance parameters specified in the most recently approved acquisition program baseline for such a program, the CAE must notify the DHS Secretary and Inspector General within five business days after such other officials are notified of the breach. If such a breach occurs, the program manager for such program shall submit to the component head, the Executive Director, and the Under Secretary in writing a remediation plan and root cause analysis. The Under Secretary shall review each remediation plan and may approve it or provide an alternative proposed corrective action. The Under Secretary shall notify the congressional homeland security committees of such breach. If a likely cost overrun is greater than 20% or a likely delay is greater than 12 months from the costs and schedule specified in the baseline, the Under Secretary shall include in such notification a written certification that: such program is essential to the accomplishment of DHS's mission; there are no alternatives to the capability or asset provided by such program that will provide equal or greater capability in both a more cost-effective and timely manner; the new acquisition schedule and estimates for total acquisition cost are reasonable; and the management structure for such program is adequate to manage and control cost, schedule, and performance. (Sec. 3) The Inspector General to study and report on the prevalence and impact of bid protests on the DHS acquisition process, particularly protests filed with the Government Accountability Office and the U.S. Court of Federal Claims.