well, just glancing at a few of the online pharmacies (the ones that ship to canada), you can get propecia for about 50$/month supply.
on evopharmacy.com, you can get proscar(the same drug, just 5 times the amount) for 73$, and that will last you a good 3 months if you cut it up into quarters.
that would probably be the cheapest way to do it if you want to stick with brand names.
if you want to do the actual propecia though, why not get a prescription from your doctor. i think it costs 50$ a month for it at the drugstore here in bc, and then you know its the real stuff.
good luck.