In a filing with the Federal Election Commission Tuesday, Day reported raising less than $11,000 in the second quarter of the year.
Day plans to challenge the Republican endorsed candidate Dr. Brian Davis in the September primary.
Davis reported raising $390,000 during the same period, including about $100,000 from his own pocket.
"When it comes to money it will be Day versus the Goliaths," Day said.
He said he would run "the old fashioned way," knocking on doors and talking with people.
Incumbent U.S. Rep. Tim Walz, D-Minn., still leads the money race in the district. But he is not as far ahead of his challengers as Minnesota's other incumbent congressional representatives.
Walz raised close about $430,000 between April and June.