0Without more context, I am guessing that it means a lot of people are involved, and by extension that a lot of money was spent. I believe this is a reference to the movies of Cecil B. DeMille, who became famous for big-budget movie spectacles with enormous numbers of extras to depict battles and Biblical events.
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"Cecil B. DeMille and a cast of thousands" originated as a reference to the big budget films produced by
DeMille. Today it is often used in reference to any big (or, more usually, insanely big) production in just about any business or even in personal interactions. Someone who is referred to as a "drama queen" might be said to be engaging in a Cecil B. DeMille production with a cast of