It depends on what the rules and terms of the bid were. Some municipalities have a rule that if the losing bid is very close to the winning bid (by "x" amount of dollars), the bidding process must be done again, or the city has the right to accept either bid.
I understand you might be concerned that somebody tipped somebody off about the bid amount, but this would be almost impossible to prove without an investigation and a witness who is willing to testify.
I used to deal with issues like this when I was a City Attorney. You could challenge the bid, but you would have to be prepared to spend a lot of money on lawyers. You would have to bring a proceeding in court, and you would have to demand depositions of the bank president and the other bidder, get phone records and documents, and hope you find the "smoking gun."
The bank, of course, would fight this action vigorously, because if you win, it basically proves that the bank president committed a crime -- bid rigging. You have to wonder why a bank president would take a risk like that to help his friend get a $50,000 contract.
If you've got any real evidence to back up your suspicions, you should talk with the District Attorney for your town. A crime may have been committed here, and having the DA investigate could possibly make your case for you.
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