It is considered the Holy Grail of comic books - Action Comics No 1 from 1938, featuring the debut of Superman.
And David Gonzales has found one mixed in with old newspapers insulating a house he was renovating in a small town in Minnesota.
Mr Gonzales did some research that confirmed the comic with a cover showing the Man of Steel holding a car over his head was valuable, though it is not worth as much as it could have been.
The book sat undisturbed in the ceiling of the house in Hoffman for more than 70 years. But a few days after he found it, Mr Gonzales said, he got into a heated discussion with his wife's aunt about its value and she wanted a share of the money.
He said he also grew irritated because every time she would turn a page, crumbs of paper would fall out. Finally he said, he grabbed it and tossed it aside, accidentally tearing the back cover. "I don't care about the money," he recalled telling her. "I don't care. It's my comic book. I can burn it if I want to."
Mr Gonzales said his wife's aunt backed down when his wife warned her he was serious.
Partly because of the damage and partly because the book shows the effects of its long service as insulation, New York-based online auctioneer ComicConnect.com said it was graded 1.5 on a 10-point scale. By comparison, an Action Comics No. 1 that was graded a nine recently fetched 2.16 million dollars (£1.4 million).
Bidding on Mr Gonzales' find was up to 137,000 dollars (£91,000) as of Friday and will close on June 11.
Mr Gonzales believes he will get about half the sale price after the auction site and the Florida comic dealer he originally took the book to get their share.
He understands the ripped cover and other damage might have shaved 75,000 dollars off the potential price. But he said "I'm not a hungry person about money", adding that he would rather work for it.