It’s not considering the value of my time; a decent (actually wearable) yarn is far more expensive than most people think.

I would consider it a waste of my time to spend a couple hundred hours on a garment that’s barely wearable because it’s uncomfortable and borderline not washable. That’s what you will get with any yarn that won’t cost you over $50 in materials for a simple pattern.

Cheap yarns are fine for beginner projects that aren’t made to be worn, but if you’re putting that much of your effort into a garment meant to be used, you should not be using bargain yarn. Your effort is worth too much to sabotage yourself that way.

eta: oh, if you’re wondering (like I did) why knitting something in polyester would be different from store-bought garments in what seems like the same material, it’s mostly in the weight of the yarn, and partly in how insanely uniform machine knitting is. That creates a radically different fabric than even the most skilled human could produce, and small deviations in either yarn weight or technique have radical differences in the fabric. There are knitting techniques that produce highly artistic texture by doing nothing but varying yarn tension.