I went to get my new perscription filled here. Yes, they are cheap, but you'll likely end up paying more in the end.
I got my perscription filed for $60, however, the glasses were uncomfortable and light sources were never properly focused. I checked with my usual optician, and it turns out they use a thick plastic material to build the lens.
Given the thickness of the lens, there were parts of it sticking out. Worst of all, my glasses were constantly giving me a headache.
In the end I went to my usual optician to change my lens (Kim's optician - yonge and Bishop)