By 1970, the CIA's Operation Momentum in Laos cost $500 million annually, equivalent to about $3.3 billion in today's dollars.
Notes on verification
Corroborated by CFR, Forbes, and Nikkei Asia sources, all citing the same $500 million annual figure for 1970 and consistent inflation-adjusted equivalent (~$3.3 billion), derived from Joshua Kurlantzick's book 'A Great Place to Have a War'.