The agreement leaves open the possibility that the operation could go to a higher bidder before the sale is finalized, trustee Irving Picard said in a statement.
The sale price is just a fraction of the $700 million that Madoff himself recently estimated the business was worth
- a figure that had been laughed off as irrational by some experts.
Revenue generated by the sale will be used to reimburse Madoff's victims.
The market-making division managed by Madoff's brother and two sons was separate from the secretive investment advisory business central to the scam. At a forum last month for victims, Picard said investigators had concluded the trading operation was legitimate and should be sold to the highest bidder.
Under the terms of the deal, Castor Pollux would take over office equipment and data of the business. The firm would pay $500,000 at closing and then payments of up to $15 million in revenues from trades through 2012.
The remaining employees of the operation were fired on Friday, but Castor Pollux said in a statement that it intends to rehire some of them if the deal is finalized.
Castor Pollux President Darin Oliver said the firm had been impressed by the sophistication of the business and the professionalism of its workers.
"The operation and employees have been extensively scrutinized by numerous federal agencies," the company's statement said.
"It has cutting edge technology and many honest and very talented employees," Oliver said. "We look forward to leveraging these capabilities into a strong and vital market making business in the years to come."
The trustee has been selling off Madoff's business assets - including works of art in his midtown Manhattan office
- to cover thousands of claims brought by victims of the former Nasdaq chairman's multibillion-dollar Ponzi scheme.