Estimates range from about 1 T$ [0] to 4 T$ [1] or 5 T$ [2].
[0] https://www.britannica.com/event/World-War-II/Human-and-mate...
[1] https://moneywise.com/life/lifestyle/financial-facts-about-w...
[2] https://www.whatitcosts.com/world-war-ii-cost-united-states-...