Belvedere Motel etc.
Oliver, hope that you don't plan on going to the Belvedere again...it was torn down a few years ago (Boo hoo hoo!) and replaced by a Canadian Tire store...
Jay's Rooming House on lower St-Hubert or Berri (forget spur of the moment like this), south of Rene-Levesque is clean, and offers reasonable 1 and 2 hour rooms.
You could get a day-room at most downtown hotels for about $50-$75 (1100-1800) depending on their occupancy rates...just give the girl your room number, she will go straight there, or, arrange room, and then get girl on street (Hotel des Gouverneurs on St-Hubert is ideal for this, as is the Lord Berri).