The cost of the Apollo project, in "then-year" dollars, was approximately $27 billion. For reference, Eisenhower's national highway system cost $100 billion.
Assuming a six-percent rate of inflation since 1969, The cost today would be about $184 billion. At 3% inflation, it would be $71 billon. This does not consider the immense advances in technology which would permit it to be done more cheaply. On the other hand it does not consider that most of the infrastructure (supplier base, etc.) have vanished because they were starved to death by the end of Apollo. So I'm calling it a push.
Anyhow, "half a trillion dollars" is an idiotic statement.
--Boris
If you follow the CPI (and what else have we got to work with, really?), $27 billion in 1969 translates to about $132 billion today. By way of contrast, the Manhattan Project cost a little shy of $1.9 billion, through the end of 1945, in 1945 dollars, or about $18.8 billion in 2002 dollars....