Americans for Prosperity, the conservative advocacy group backed by the Koch brothers, is running Obamacare attack ads featuring a cancer patient who claimed her treatments were "unaffordable" under the new health care law. On Monday, The Detroit News reported that the patient will actually save more than $1,000 a year.

Julie Boonstra says in the anti-Obamacare ad that she was diagnosed with leukemia five years ago, and her health care plan was canceled when Obamacare went into effect.

"Now, the out-of-pocket costs are so high, it's unaffordable," she said.

Before her plan was canceled, Boonstra was paying a $1,100 monthly premium. That's $13,200 a year, without adding out-of-pocket expenses like co-pays and prescription drugs. But under her new plan, the Blue Cross Premier Gold, Boonstra's premiums are down to $571 a month, and out-of-pocket costs are capped at $5,100. That's a maximum annual expense of $11,952 a year.

According to The Detroit News, Boonstra said it “can’t be true” that her new coverage is cheaper than her old.

“I personally do not believe that,” Boonstra said.

The ads set out to target Rep. Gary Peters (D-Mich.), who faces former Michigan Secretary of State Terri Lynn Land (R) in a tight race for Michigan's U.S. Senate seat. Peters voted in favor of the Affordable Care Act.

The billionaire Koch brothers have spent millions in attack ads in Michigan and beyond, prompting Senate Majority Leader Harry Reid (D-Nev.) to take a public stand against their tactics. Reid accused the Kochs of "trying to buy America," and said Republicans are "addicted to Koch."

Boonstra told The Detroit News she had never been politically active before joining the anti-Obamacare campaign. The newspaper reported her ex-husband, Mark Boonstra, had served as chair of the Washtenaw County GOP, and was appointed by Gov. Rick Snyder (R) to the Michigan Court of Appeals in 2012.