Usually 20$ if i really enjoyed the session and didn't had to pay extras/the price was not higher than regular Montreal prices
If i pay an extra, usually i consider it a tip in a way
If the price is higher than Montreal norm, im really paying a "prenium" for that session so... lol
But its a case by case, sometimes i may only give a 10, sometimes nothing at all if im a bit more "low" on money because of whatever reason.
But really i try to include a little something when possible.