Otago University researchers have found the average new law costs $3.5 million to produce.
The study's lead researcher Nick Wilson says in most cases laws save more money than they cost to produce.
But he says some issues could be dealt with more cheaply by using education and media campaigns.
Mr Wilson says his team is creating a model that politicians could use to estimate the cost-effectiveness of a law before introducing it to Parliament.
He says money is also being wasted on member's bills that have no hope of becoming law.