Staff at New Zealand's market watchdog have spent nearly 13,000 hours so far working on the Viaduct Capital and Mutual Finance case.
The Financial Markets Authority has also paid more than $1.65 million to external lawyers, investigators and other support services for the case.
The trial of four directors of the two failed companies was aborted in May after running for nine months.
This was because thousands of documents were provided to the defendants late.
The FMA - the prosecutor in the case - has confirmed it will push for a retrial of three of the four directors, Paul Bublitz, Bruce McKay and Richard Blackwood.
The FMA, under the Official Information Act (OIA), last month released a breakdown of external costs in the case so far.
Since mid-2011 when the FMA's probe began, more than $1.65m has been paid to outside parties for this case.
That includes more than $560,000 paid to law firm Meredith Connell, which is acting for the FMA.
It also includes more than $883,000 paid to professional services firm Deloitte which was involved in the Viaduct and Mutual investigation.
In response to a further OIA request, the FMA calculated it had spent $1.93m internally on the case up to the middle of June.
However, the FMA's head of policy and governance Joanne Davis-Calvert said this figure was representative and specifically used to reply to OIA requests.
"We do not record, store or use this information ourselves, as the calculation does not involve any actual 'cost' (unlike the external costs, which are paid to external providers) ...on reflection, as we believe the 'internal cost' calculation may be misleading will not continue to calculate these costs...," she said.
Davis-Calvert said the FMA did record how much staff time had been spent on litigation matters and that 12,721 hours had been spent on the Viaduct and Mutual case since 2011.
McKay and Blackwood served as directors of Viaduct Capital while Bublitz was Mutual Finance's board. The firms went into receivership in 2010, owing $17m.
Bublitz, according to prosecutors when the trial began last August, allegedly used the two finance companies to support his property investments.
The other defendants in the case were accused of helping him.
All the defendants denied the allegations against them and say they will continue to defend themselves in a re-trial.