The Serious Fraud Office spent $1.3 million on consultants and contractors in the most recent financial year - up from less than $100,000 three years ago.
Most of the money was spent on forensic accountants and investigators who the white-collar crime agency said were needed to help with a large number of cases including six finance companies, such as South Canterbury Finance and Hanover, in the past 18 months.
Criminal charges were laid in five finance cases, and Hanover is still under investigation.
According to figures released under the Official Information Act, the external spending increased from $97,356 in the 2007/08 financial year to $1,318,967 three years later.
Accounting firms to secure lucrative deals include Deloitte ($213,817), KPMG ($151,213) and KordaMentha ($98,709).
In the first three months of this financial year, the SFO spent a further $369,463, with nearly $100,000 of that paid to a private investigation firm, Omega Investigations.
The marked rise in payments to contractors and consultants was a result of significant investigations, including South Canterbury Finance, Hanover, Belgrave Finance, Dominion Finance, Capital + Merchant Finance and Rockforte Finance.
"The complex nature of these cases requires specialist skills which have, in part, been met from external providers," the SFO said.
"SFO is now decreasing its dependence on external providers by recruiting additional forensic accountants, investigators and lawyers," the agency said in a statement.
The extra resources also led to 84 per cent of inquiries being completed within 12 months and the average inquiry length of less than six months, according to the SFO.
Staff numbers are likely to increase from 40 to 50, as the SFO budget will be given an extra $7.5 million over the next three years.
The $1.3 million spent in the 2010/2011 financial year also came after SFO director Adam Feeley was appointed in late 2009 and restructured the agency, which led to four senior staff being made redundant.
"If that experience was to be lost, it would be very hard to replace those people who have had ... a unique experience fighting white-collar crime in New Zealand," one Queens Counsel said during the restructuring.
Three of the senior staff - Gib Beattie, Ian Varley and David Osborn - had nearly 50 years of SFO experience and have since started their own forensic investigation firm, Beattie Varley & Associates.
Another 11 staff have resigned since September 2009.
At the time of the restructuring, Mr Feeley told the Herald the need for change was endorsed by other law-enforcement agencies, regulators and the insolvency sector, as well as major legal and accounting firms.
Big crime, big costs
Consultants' and contractors' costs:
* 2007/08: $97,356
* 2008/09: $200,872
* 2009/10: $401,926
* 2010/11: $1,318,967
* July-October 2011: $369,463