Cost of US WWII Aircraft
Note that the aircraft listed below are all Army Air Forces aircraft, with the original source being the Air Technical Services Command, Budget and Fiscal Office.  To date we have not been able to find any information anywhere in all of the literature and web sources on costs of US Navy Aircraft, with the exception of the Grumman F6F Hellcat, where I did see on one web page the cost being $50,000.  This cost does make some since as it was a high production aircraft and has comparable cost to the P-51. 

The costs given by the Air Technical services are "average cost per airplane is the weighted average cost on all programs approved during a designated fiscal year and represents the estimated cost of a complete airplane ready for flyaway, including factory installed ordinance and radio equipment." 

All values are in US Dollars.  To figure what the aircraft would cost in 2009 dollars use the following information:
1941 Cost X 14.72; 1942 Cost X 13.27; 1943 Cost X 12.5; 1944 Cost X 12.29; 1945 Cost X 12.02.

A P-51 Mustang built in 1945 at $50,985 times 12.02 would cost $612,839.70.  Compare this to the $140 million the F-22 costs today.