I don't know what your budget is or how you're getting to Montreal, but check these guys out.
Calgary Car rental Canada Vancouver car rental Toronto cheap
Despite the name, the vehicles aren't shit. We rented a van through them last year and drove the crew to B.C. Ended up with a 2006 Ford Winstar. They're the cheapest car rental place you'll find and really easy to deal with. Also, with 4 of you splitting the cost, might fall into your price range.
Just make sure you have a driver that's cool with staying sober, and a fully stocked cooler for yourself and the rest of your crew