Where to get plexiglass/glass for DIY frame: GTA

I have started to make frames. I can do the matt cutting myself and cut the frame. But I haven't seen a place in the GTA where I can get cheap plexiglass for the front of the frame?

I have seen some places that sell acrylic but it's super expensive, because it seems like it's pretty thick. It seems cheaper to go to Ikea and buy a frame and just use the plastic from that frame. But I don't like that option. There must be a good place I can buy cheap thin plexiglass/plastic downtown Toronto.

Much appreciated!