The Republican Iowa caucus is on track to be the most expensive ever in the state, despite former President Donald Trump's dominance in the polls.

The battle to win the Republican Iowa caucus is the most expensive on record, with over $120 million spent on ads by the campaigns and their affiliated political action committees in the Hawkeye State, according to data provided to CNBC by AdImpact.

The massive amount of resources placed into Iowa reflects how competitive candidates and their allies still believe the GOP nomination race to be, despite Donald Trump’s dominance in the polls. Going into Monday’s caucus, Trump’s lead over his closest rival, former South Carolina Gov. Nikki Haley, averaged 33 percentage points, according to a Real Clear Politics polling aggregation.

Around $84 million of the $120 million total ad buys came from campaigns and allies of the top three candidates, Trump, Haley and Florida. Gov. Ron DeSantis, according to the data. The figure includes television, radio and digital spots.