If you are near Dundas West Stn, the cheapest place to get this is Bike Pirates (1564 Bloor St. W)
They have very limited hours for new part purchases:
Just bring the caged bearings with you, and ask for a new replacement.
Bike Pirates is a non profit DIY bike repair place, so pretty much guaranteed you would get it for cheapest price.
If on the east end, try Bike Sauce (check website for their limited service hours)