OTTAWA -- Running to replace Stephen Harper as leader of the federal Conservative party promises to be an expensive proposition.

Rules released by the party on Tuesday allow candidates to spend up to $5 million on their campaigns. As well, they must put up a $50,000 registration fee and a $50,000 "compliance" fee to enter the race.

The spending limit is more than five times the $950,000 ceiling for the Liberal leadership campaign in 2013. The NDP imposed a limit of $500,000 in 2012.

It will also be a long campaign, with the new Conservative leader to be picked on May 27, 2017. The Liberal campaign was five months long, the NDP race six months.

Candidates must be Tory members for at least six months when they enter the contest.

The party will not follow the example of the Liberals, who let non-members vote for their leadership. Only Conservative members will be allowed to cast ballots in the 338 ridings, and they will have to pay for their own memberships.

Each riding will carry equal weight in picking the new leader.

The leadership became vacant Harper resigned following the Conservative defeat in the October federal election.

Rona Ambrose was chosen to fill in on an interim basis with the understanding the interim leader would not enter the race.

No one has declared their intention to run, but polls have named former cabinet minister Peter MacKay as an early front-runner.

Others mentioned as possible candidates include former cabinet ministers Tony Clement, Jason Kenny and Lisa Raitt, along with businessman and television personality Kevin O'Leary -- who likely would have to take out a membership and wait the six months required by the rules if he decided to run.

Candidates must register by Feb. 24, 2017.