The effort to hold Canada's allegedly free-spending senators to account has a new price tag — and it's a whopper.

The independent audit of Sen. Pamela Wallin's expenses has cost taxpayers $390,058, nearly three times the amount of ineligible expenses which she was required to pay back, Senate officials disclosed Friday.

It's also more than twice the total cost the auditing firm in question, Deloitte, billed for its review of expense claims filed by senators Mike Duffy, Patrick Brazeau and now-retired Liberal Mac Harb.

How $43K became $390K

  • Audit length: Jan. 3, 2013 to Sept. 30, 2013.
  • Original value of the Deloitte contract: $43,408.
  • Additional cost of the contract after the first two quarters: $83,650.
  • Additional cost during the third quarter: $263,000.
  • Total cost of Deloitte contract into Wallin's expenses: $390,058.
     

The audit into their living allowances and expenses cost $138,784.

"We know this is a significant cost," said a statement from Sen. Gerald Comeau, the Conservative chairman of the Senate's board of internal economy, which oversees contracts and spending.

"However, once the audit was ordered, we had to allow it to be fully concluded in order to get a fair and consistent reading of the issues involved."

The figures represent just the latest revelations in the Senate spending scandal, which has gripped Ottawa for months and comes with the upper chamber nearing a vote next week on a motion to suspend Wallin, Duffy and Brazeau.

Costs soared as probe expanded

In Wallin's case, costs soared after the Senate asked auditors to expand their probe of her expenses — primarily travel costs — to include her entire time in the upper chamber, which was not done in the other three cases.

The initial cost of the audit was pegged at $43,408, but it took longer to complete than originally estimated, driving the price up by an additional $83,650 to $127,058 at the end of the second quarter.

Over the summer, costs jumped by another $263,000, bringing the total cost of the audit into Wallin's expenses to $390,058 by Sept. 30, the end of the third quarter.

The audit costs are found in a routine Senate document released Friday that lists contracts worth more than $10,000.

Liberal Sen. George Furey, the former deputy chair of the committee, also said it was necessary to get an independent assessment.

"The cost of conducting these audits has to be viewed in context of the larger issue of public accountability and trust," he said in a written statement.

Neither Comeau nor Furey were immediately available for an interview Friday.

With files from CBC's Susana Mas