NDP Leader Thomas Mulcair has accused Stephen Harper of spending $1 billion on the Senate while prime minister.

At a campaign stop on Thursday, Mulcair said that Harper "spent $1 billion on the Senate. I'm going to try and make sure Canadians never spend another penny (on it)."

Harper was first elected as prime minister in 2006, but the Senate's annual financial statements posted online only go back to 2010. According to those statements, the net cost of its operations has averaged approximately $105 million per year. That would indeed eclipse the $1 billion mark over 10 years of Harper’s tenure.

However, Senate costs have actually declined year-by-year in the last five years. The Senate's annual net operating costs are as follows, with each fiscal year ending on March 31, according to the Senate's financial statements:

Those 2012 and 2013 costs include the less than $1 million in questionable expenses identified in the auditor general's report earlier this year, which examined records from March 31, 2011 and April 1, 2013.

The actual cost of the auditor general's report accounts for one of the more significant one-time expenses accrued by the Senate in recent years. Michael Ferguson, Canada's auditor general, said last June that the audit cost $23.6 million, or roughly $12 million more than the cost of the Senate's typical yearly audit. That additional expense was not paid for by the Senate.

As for the costs of the senators themselves, each of Canada's 105 senators currently make a base salary of $142,400, with additional pay afforded to those in positions of authority. Sen. Claude Carignan is the highest-earning senator as Leader of the Government in the Senate, with a salary of $222,500.

Correction: An earlier version of this story incorrectly quoted Mulcair as saying he would save $1 billion by abolishing the Senate.