A Minnesota contractor who was gutting a dilapidated home he'd bought to renovate got more than he bargained for when he opened up the walls: He came across a 1938 comic book featuring a new hero named Superman.

David Gonzalez was intrigued by the rare copy of Action Comics No. 1, which introduced the iconic Man of Steel to the world. Gonzalez did some research and found out his find could be worth a pretty penny.

The website of Comic Connect, the Manhattan-based Internet vintage comic auction house that's selling Gonzalez's hidden treasure, described it as "holy grail of Superman comic books."

The auction opened on Monday. As of Thursday night, there were 34 bids on the comic, with the highest bid being $127,000.

The comic could have been valued at far more, but it was damaged when an excited relative handled it too roughly. Gonzalez, 35, told ABC News that his wife's aunt kept touching the book and handling it, resulting in tears to the back cover.

Vincent Zurzolo, the chief operations officer for Comic Connect, told ABC News that the comic was valued at about $150,000. On an industry scale that ranks a comic's condition from 1 to 10, Gonzalez's comic was a 1.5. Had it not been torn, it could have been worth an estimated $75,000 more.

"It's quite an expensive tear," Zurzolo said.

Comic Connect sold a near-perfect copy of an Action Comics No. 1 for $2.16 million.

Gonzalez, a married father of four from Hoffman, Minn., paid $10,100 for the house where he found the comic.

A nearby restaurant had wanted to buy the vacant home for $10,000 in order to knock it down and build a parking lot. Gonzalez saw a renovation opportunity and offered the property owner $100 more than the restaurant had.

Gonzalez said when he renovates homes, he always puts money inside the walls as a treat for any future renovators.

"The irony here, obviously, is all these years he's been putting money behind these walls and now he finds this treasure trove behind a wall," Zurzolo said. "It's an exciting story. It's really wonderful for my company to be a part of this."

The auction closes on June 11. Zurzolo will get to keep 90 percent of the final sale price, and Comic Connect will get a 10 percent commission.

Gonzalez said the money won't change him. He doesn't even plan to go on a big spending spree.

"I'll fix my house … upgrade my tools," he said.

He also plans to finance his children's education, and he wants to buy a Chevrolet Camaro - a used one.

Deanna Gonzalez, David Gonzalez's wife, still can't believe the excitement of the past few days.

"It's crazy," she said. "I never expected anything like this to happen to us."