• The battle to win the Republican Iowa caucus is the most expensive on record, with over $120 million in ad spending by campaigns and their affiliated political action committees.
• Around $84 million of the total ad buys were in support of the top three candidates, Trump, Haley and Florida. Gov. Ron DeSantis,
• The massive amount of resources put into Iowa this time reflects how competitive candidates and their allies still believe the race to be, despite 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.

Among the top three, Haley and her allies have spent the most: $37 million in Iowa alone.

Despite Haley's advantage in the Iowa ad spending wars, Trump is clearly not taking his massive polling lead for for granted, however.

Together, the former president's campaign and the outside group supporting him, Make America Great Again Inc., have aired around 21,000 TV ads this cycle. This is roughly equivalent to the 22,000 spots the Haley team has paid to broadcast, according to data by Wesleyan Media Project, reviewed by CNBC.

"Judging by the number of ads placed in Iowa and New Hampshire, Trump's campaign is not taking those states for granted," Michael Franz, co-director of the Wesleyan Media Project, said in a statement released with the report.

Haley and DeSantis' allied groups in Iowa are paying for more than just ads.

Americans for Prosperity Action, a super PAC backing Haley and financed in part by billionaire Charles Koch, said they planned to knock on 50,000 doors in the eight days between Jan. 7 and Iowa Caucus day.

The group told CNBC they have more than 150 staff and volunteers throughout the Hawkeye State, working to build support for Haley. In addition to the volunteers, AFP Action has spent over $900,000 on pro-Haley ads targeting Iowa voters, according AdImpact.

Nonetheless, the group appeared to be managing their expectations for Monday night.

"While Iowa and New Hampshire are important, we're building for the long-term. We're already up with advertising and one-on-one grassroots outreach in South Carolina and a number of Super Tuesday states," Bill Riggs, a spokesman for Americans for Prosperity Action, told CNBC in an email.

"The DeSantis team has made clear they need Iowa to survive. Our goal is to help Nikki Haley finish strong and keep the momentum going into New Hampshire," said Riggs.

DeSantis' campaign and two outside allies have spent a combined $30 million on TV, digital, and radio ads in Iowa. But they have also been active in door knocking and engaging with voters in Iowa.

One of the two DeSantis super PACs, Never Back Down, has knocked on over 915,000 doors in the Iowa, according to the organization.

As for Trump's super PAC, MAGA Inc. would not provide data on what efforts they've made outside of their ad spending in support of the former president.

"We'll leave the pre-election backslapping to others," Taylor Budowich, the head of the super PAC, told CNBC. "I have no interest in telegraphing strategic or tactical efforts to the media."