• Marshall Plan: Cost: $12.7 billion, Inflation Adjusted Cost: $115.3 billion
• Louisiana Purchase: Cost: $15 million, Inflation Adjusted Cost: $217 billion
• Race to the Moon: Cost: $36.4 billion, Inflation Adjusted Cost: $237 billion
• S&L Crisis: Cost: $153 billion, Inflation Adjusted Cost: $256 billion
• Korean War: Cost: $54 billion, Inflation Adjusted Cost: $454 billion
• The New Deal: Cost: $32 billion (Est), Inflation Adjusted Cost: $500 billion (Est)
• Invasion of Iraq: Cost: $551b, Inflation Adjusted Cost: $597 billion
• Vietnam War: Cost: $111 billion, Inflation Adjusted Cost: $698 billion
• NASA: Cost: $416.7 billion, Inflation Adjusted Cost: $851.2 billion

TOTAL: $3.92 trillion

As a matter of fact, the only single thing that comes even vaguely close (but still isn’t as huge) is the entire US cost of WWII!

the total cost now exceeds $4.6165 trillion