This option illustrates the cost implications of such a force-structure mix by replacing Air Force purchases of manned F-35 aircraft (also known as the Joint Strike Fighter) on a one-for-one basis with UCAVs. The Air Force is currently scheduled to increase annual production of F-35s from six planes in 2007 to 110 by 2014. This option assumes that the Air Force would reduce F-35 production to a peak rate of only 88 planes per year and purchase UCAVs instead. Thus, this option would replace 56 Air Force F-35s with a like number of UCAVs over the 2006-2015 period and would ultimately replace 298 of the 1,763 F-35s planned for the Air Force through 2027. The Congressional Budget Office assumed that UCAVs would begin replacing F-35s at a rate of four in 2012, eight in 2013, and 22 per year thereafter. (The option also assumes that an additional 20 UCAVs per year would be bought for other missions, but their costs are not included in the table above.)
http://www.cbo.gov/bo2005/bo2005_sho...m?index=050-17