When travelling in North America I will always save cash on hotels for "miscellanious expenses" (cabs, drinks, food).
The Quality Inn Downtown Montreal offers fantastic rates, I think I paid $80 for a double room with king bed and pull out bed. The room itself was large, and we had a great balcony with a view of Montreal and the st lawrence (tenth floor is great). The room itself was very basic as you do get what you pay for and this is an older building without many if any upgrades - but it was clean and oh so convenient for my visit to Montreal.
Staff was also great and answered our various questions which usually consisted of "How do we get here" and "Where is open in terms of nightclubs tonight?"
I would stay again.