Romney is worth at least 190 million dollars and has spent more than 17 million dollars of his own money on his bid for the GOP nomination.
That includes about two million for ads in South Carolina, where Thompson told a crowd at a restaurant that Romney "can't buy" the state.
Romney says he's putting in the hard work necessary to win the early primary state. He's getting in a dig at Thompson, who some suggest is a lazy campaigner.
Thompson yesterday also slammed Republican rivals for supporting a failed immigration bill that was backed by President Bush. The former Tennessee senator misspoke: top candidates Rudy Giuliani and Romney have criticized the measure at various debates and campaign stops. Only John McCain supported it and he has since qualified his position, saying tough border security must come first.