More than $48 million in independent expenditures, most of it from outside the Sunshine State, has been spent on the Rubio-Murphy race in which the Miami Republican has held about a 3 point lead in recent days, according to the polling average on realclearpolitics.com.
Only five other U.S. Senate campaigns -- in Pennsylvania, New Hampshire, Nevada, North Carolina and Ohio -- have received more money from outside their campaigns.
Every state except Nevada features incumbent GOP senators who, like Rubio, are trying to fend off Democratic challengers. Nevada's race is for an open Senate seat vacated by the retiring Senate Minority Leader Harry Reid.
Those six races will likely decide whether the Republican Party retains the Senate majority it gained in the November 2014 elections.
In addition to money contributed by outside groups, Rubio's campaign had raised $12.48 million through Oct. 19 while Murphy's campaign had raised $13.72 million, for a total of $26.2 million, according to the Federal Election Commission.
That figure combined with the independent expenditures puts an overall price tag of almost $75 million on the Rubio-Murphy Senate race.
In Florida's Senate race, outside groups have made 14 TV, media and digital ad buys totaling at least $1 million, all but one of them targeting Murphy.
The biggest buy was made by the Senate Leadership Fund on Oct. 27 for $3.16 million.
Other groups based outside Florida that have spent big against Murphy are the American Future Fund, the U.S. Chamber of Commerce, the National Republican Senate Committee and the National Rifle Association.
The only Florida-centric organization with significant expenditures opposing Murphy is the Florida First Project, a super PAC created in June on the day Rubio did an about-switch and announced he was running for Senate re-election after having declined during his earlier presidential bid.
So-called "super" political action committees are free to collect unlimited amounts of money as long as the donors' identities and the amounts of their contributions.
The flood of independent expenditures by super PACs has followed a landmark 2010 Supreme Court ruling, in a case brought by the conservative watchdog group Citizens United, that described such spending as expressions of free speech protected by the First Amendment.
However, direct contributions to political campaigns remain limited by campaign-finance law.
Photo credit: Wilfredo Lee, Associated Press