Reality TV star Dan Dotson from the US show Storage Wars said he just discovered that he sold a storage unit containing $US7.5 million ($A10 million) in cash for a measly $US500 ($700).

Dotson and his co-star wife Laura told The Blast that a random woman approached him at one of his auctions about the multimillion-dollar finding last week.

“She walked up and told me her husband works with a guy who bought a unit from me for $US500 and found a safe inside,” Dotson said, according to the New York Post.

The woman said the new unit owner, who wasn’t identified, took the safe to a locksmith who broke it open and discovered $US7.5 million in cash.

Things got complicated when the new owner was contacted by a lawyer representing the former owners, who offered a $US600,000 ($A828,000) reward in exchange for the cash.

The new owners declined the initial offer before settling on $US1.2 million ($1.65 million) to return the remaining $US6.3 million ($A8.7 million).

The Dotsons’ co-star, Bargain Hunters Thrift Store owner Rene Nezhoda, said the cash was most likely mafia or drug cartel-related.

“If you find money like that, there’s probably a reason it isn’t in the bank,” Nezhoda told The Blast.