Chicago Pile-1 (CP-1) was the world's first artificial nuclear reactor, designed and built as part of the Manhattan Project during World War II. It was located under the stands of Stagg Field at the University of Chicago and became operational on December 2, 1942. CP-1 was constructed by a team of scientists and engineers, including notable figures such as Enrico Fermi, who led the project.
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Getting funding for the Chicago Pile Edward Teller interview by Web of Stories (1996)
Source. - youtu.be/mnScq24BEmc?t=114 the main cost for the reactor was the graphite. Presumably they already had the uranium in hand?. Edit, no, it is because it was a specialized graphite: Video 2. "German graphite from The Genius Behind the Bomb (1992)", i.e. nuclear graphite.