Republican U.S. Senate candidate Kurt Bills raised more than $105,000 during the first 25 days of July, but his campaign is struggling to stay afloat financially as he racks up cost in his bid to unseat U.S. Sen. Amy Klobuchar.

At the end of the latest fundraising period, Bills' campaign reported having $5,841 in the bank after spending much of his funds on polls, consultants and the red, white and blue campaign bus he uses to crisscross the state, according to the latest reports filed with the Federal Election Commission.

Heading into next week's primary election, Klobuchar has $5.4 million banked for her re-election bid, more than 920 times more cash than Bills.

While Klobuchar has been collecting campaign donations since the start of 2011, Bills only entered the race this winter and has struggled to narrow Klobuchar's fundraising advantage. Bills began the month of July with less than $65,000 in the bank and spent more than $160,000 before month's end.

A recent survey by Public Policy Polling indicates that Klobuchar, a first-term senator, is heavily favored to defeat Bills, a state representative and high school economics teacher.

Klobuchar has spent more than $2.4 million and raised more than $5.7 million this election cycle.

As of July 25, Bills had not yet raised $400,000, but U.S. Rep. and former presidential candidate Ron Paul and his son, U.S. Sen. Rand Paul, held a fundraiser for him in Washington, D.C., late last month.

Klobuchar and Bills will compete in the contested DFL and Republican primaries on Tuesday but, with the endorsements of their respective political parties, both are expected to advance to the November general election.