Approximately $2.1 billion.

" The Space Shuttle Endeavour, the orbiter built to replace the Space Shuttle Challenger, cost approximately $1.7 billion." Source and further information: http://www.nasa.gov/centers/kennedy/about/information/shuttle_faq.html#1 "The table below shows the costs of the Space Shuttle program from its inception through 2003 (in 2003 $). The data come from a paper of mine in 1994 (1971-1993) and the Gehman report on the Columbia accident (1994-2003). The data show that the space shuttle program has cost $145 billion over its existence and about $112 billion since the program became operational. The average cost/flight has been about $1.3 billion over the life of the program and about $750 million over its most recent five years of operations. According to the FY2006 NASA budget request the Space Shuttle program is expected to cost (in millions of 2004 $) through 2010: 4060.9 2004 4543.0 2005 4530.6 2006 4172.4 2007 3865.7 2008 2815.1 2009 2419.2 2010 Because NASA has costs for the Shuttle program that are not reflected in the shuttle line item, it is appropriate to add 10% to these totals (see Pielke, 1994 for discussion) and also to adjust to 2003 dollars (to make consistent with the data table). If the program is terminated after 2010, then it will have a total lifetime costs of $173,423 million or about $173 billion. If the program averages 4 flights per year upon a return to flight, then the shuttle will fly an additional 22 times, for a total of 134 flights over its lifetime. This will result in a total program cost per flight of $1.3 billion. Interestingly, the average cost per flight from 2004-2010 is also $1.3 billion. The average cost per flight from the middle of 2005 through 2010, assuming 22 flights, is about $1.0 billion." Source and further information: http://sciencepolicy.colorado.edu/prometheus/archives/space_policy/000346space_shuttle_costs.html