If enacted, the Coronavirus Aid, Relief, and Economic Security Act (CARES Act) will be the single most expensive piece of legislation in U.S. history.
His New Deal, which was actually a large number of bills passed over several years rather than a single piece of legislation, cost $41.7 billion in 1933 dollars, which is the equivalent of $856.1 billion today.
Marshall Plan - $144 billion, adjusted for inflation
The Marshall Plan cost $13.3 billion when enacted -- the equivalent of $144 billion in 2020 -- and was signed into law by former President Harry Truman in April 1948.
Great Recession laws - $1.8 trillion combined, adjusted for inflation