Investigators have amassed three roomfuls of documents and have interviewed 600 witnesses in the case, in which Mr Ng, a martial arts expert, faces 12 murder charges, after charred bones and an alleged torture bunker were unearthed in a remote mountainous area in California. The bill so far is more than $6m ($3.8m), double that of the Simpson case - and the trial has yet to begin.
Its costs became a critical issue, as the case was transferred to Orange County in southern California because of the huge publicity in the area where the alleged crimes were committed. Last year, the county - once one of the richest in the United States - went bankrupt in a securities and derivatives dealing scandal, and is $2bn in debt.
Mr Ng, 33, a former pupil of Bentham Grammar School in north Yorkshire, became one of America's most wanted men after police found hundreds of human bones scattered around a property in Wilseyville, 125 miles east of San Francisco. They also discovered three decomposing bodies; a cabin, containing handcuffs and a whip, which could be viewed from outside through a one-way mirror; and videotapes which allegedly show Mr Ng torturing women victims. His alleged accomplice, Leonard Lake, whom police have linked with 20 murders, died in police custody by swallowing a cyanide pill.
The case began in 1984, when Mr Ng was arrested in Canada after shooting a security guard while attempting to rob a hardware store. After a six- year extradition battle, he was returned to the United States, where his case became bogged down in legal arguments, including a fight over the authorities' decision to place him in a cage for court appearances. Mr Ng was born in Hong Kong but spent part of his childhood in Lancashire before emigrating to the US. A martial arts, fanatic, he joined the US Marines, but was thrown out for stealing weapons.
Officials say the trial, which may not begin for another two years, will be one of the most expensive in the history of California, a formidable claim given the number of elaborate high-profile cases held in the Golden State in recent years (OJ Simpson, the Menendez brothers, the Rodney King affair, Charles Manson, and John DeLorean.) However, relief is in sight for worried Orange County officials; the state has pledged to pick up the tab.