They may be poor down in Trash Holler, but the swimmin' hole's got real blue water.
Cash me if you can! he says, which could have two meanings: sell my corpse to a medical research firm, if you can find some Burke-and-Hare types to act as the middleman, or catch / cash me, meaning, seek to equal or surpass me. Which is impossible, given that the poor children have no hope of amassing a fraction of Richie's capital, and would be forever behind him as his accumulated wealth earned more interest.
Or "catch" in the sense of "stop, contain," in which case they'll have to grow up and go into politics and raise the ire of the people against the Richs, denanding the distribution of their property.
Or, just another money pun. That's all he said. God, what a tiresome bore.