Symbolism, Imagery, Allegory
Yes, we know: in Econ 101, the instructor said, "Money is a symbol. A symbolic medium of exchange." But we're not talking about that here.
There's a lot of money exchanging hands in the stories in Go Down, Moses. There's the betting in "Was," for example, or the buried gold Lucas obsesses about in "The Fire and the Hearth"; the banknotes in the envelope in "Delta Autumn"; the funeral money being collected in "Go Down, Moses"; the McCaslin inheritance.
These stories are all about the legacy of slavery in the South, and the money exchanging hands here is connected to that legacy. So, the money in these stories is either literally (not symbolically) the money paid for a slave (in "Was" and in "The Bear," for example) or a symbol of reparation.
Lucas seeks buried money, partially as payback for the inheritance he believes he was denied. Roth is trying to "pay off" his retribution to the woman who has had his son, but of course money itself can never be sufficient retribution. In "Go Down, Moses," the money collected for Samuel Beauchamp's funeral (7.2.50) is again symbolic of retribution: the white merchants feel they must pay in some way.