Painting on cheap canvas is a waste of art. This will soon split, rip or crumble; not a product a collector will want to invest in. I buy good quality primed canvas by the roll; good canvas is not that expensive when bought in bulk. It’s an investment at once, but easily saves me thousands of dollars once I have used it all.
Canvases of very large size need good quality stretchers that will not break when pulling canvas on them, or warp with time. But smaller size canvas can cope with lighter stretchers, especially if planning to frame your artwork; recycling old and cheaper canvases is a good way to save you some money.
The two canvases in the video I have collected from the rubbish, but I do advice to not recycle stretchers that have been out in the rain as these will most likely warp.