Congressional Budget Office Cost Estimate: H.R. 5235, Emergency Iron Dome Replenishment Act [open pdf - 94KB]
From the Document: "H.R. 5235 would authorize the President to assist Israel with the production, maintenance, and sustainment of its Iron Dome anti-missile defense system. The Department of Defense (DoD) plans to provide such assistance to the government of Israel through 2015. Over the 2011-2014 period, DoD transferred $634 million to the government of Israel to develop and procure interceptors and components for the system. In addition to that amount, on August 1, 2014, the Congress provided $225 million in emergency appropriations to help Israel replace interceptors. Based on the budget request for 2015 and the U.S.-Israel Iron Dome Procurement Agreement, CBO estimates that another $176 million would be provided to Israel in 2015, assuming appropriation of that amount. Pay-as-you-go procedures do not apply because enacting the bill would not affect direct spending or revenues."
Congressional Budget Office: https://cbo.gov/