Not sure what cab you are using, but everytime i used a cab in MTL its just so over priced... even for very short distance. So much i decided to not use them anymore, unless total nessesity. Subway on the other hand is pretty good, for a small 3$ you can use both SUBWAY AND BUS to get where you want, only thing is you need to not be too much in a hurry, because the bus is less conevient than the subway in term of wait time.
Also i think subway close around 1:30 am even on week end, so better not go to a bar too far... Wish the subway would be open til at least 4 am on week end... seem only normal.
Now as for drinking and driving, of course you DON'T !! Its not about the fine, think about the security first, both of yourself but also of the others.