Gingrich made the comment Sunday after attending Mass at the St. Ambrose Cathedral in Des Moines.
Gingrich said the amount that the former Massachusetts governor will spend over his various campaigns will rival that spending of billionaire New York City Mayor Michael Bloomberg.
Gingrich said he believes that "Romney would buy the election if he could."
A political action committee supporting Romney has rolled out ads attacking Gingrich in the days before Tuesday's caucuses.
The former House speaker is set to make three campaign stops later Sunday in Iowa.