budget dust n. money said to be insignificant when compared to other (planned) expenditures. (source: Double-Tongued Dictionary)
Further reading
While reading Great Expectations (Bookshop|Amazon) by Charles Dickens, a listener in Arlington, Texas, is surprised when one of the characters inherits some money, which Dickens describes as a cool four thousand. Were they really using cool that way...
Among the proverbs in Leo Rosten’s Treasury of Jewish Quotations (Amazon): If you drop gold and books, pick up the books first, then the gold. This is part of a complete episode. Transcript of “Who Is Just Carrying Around Gold, Anyway...