The closer the parking is to the airport, the more expensive it is.
The best is Econoparc P6 to P9, which costs $30 a day and is located directly on the site of the Montréal-Trudeau airport. In contrast, ValetParc is $50 a day, with a valet to look after your car.
Park'N Fly, on the other hand, is further away and costs from $22 a day, including a shuttle that takes you to the airport in 10 minutes.