"I was against earmarks before being against earmarks was cool," he said.
The Democrat responded that Sanford had years ago told her he supported trade and dredging.
"You didn't tell the truth," she told Sanford. "You turned around and did the opposite."
Colbert Busch also said that, if elected, she would return 10 percent of her congressional salary to the government.
The candidates also differed over issues such as immigration reform, the federal health care overhaul and abortion during the debate sponsored by the Patch news service, the South Carolina Radio Network, Charleston television station WCBD and which was telecast by C-SPAN.
Sanford tried to tie Colbert Busch to House Democratic Leader Nancy Pelosi and labor unions. She said she was independent and planned to represent the district's voters, first and foremost. The debate, attended by 500 people, was frequently interrupted by applause and shouts from the audience.
"We're at an incredible tipping point as a civilization and I think if we don't get spending right in Washington, D.C., there will be real consequences," Sanford said. "I've gotten into this race with the hope of taking what I've learned in Congress, what I learned in the governorship and what I've learned on the way up and on the way down and applying it to what I believe is the great debate of our civilization, which is indeed, how do we get our financial house in order."