@Reynard My mum used to make cushion casings from any suitable material, and would cut a worn bedsheet down the middle, and sew it back together with the outer edges swapped to the centre, to get some more wear out of it. She also would pick up stuff from the jumble sale for pennies, to pick apart and keep the material for repair patches. As a kid, every time I put a hole in the knee of my trousers, they received a repair patch and I received a bollocking.
TBH, I've not noticed much difference in durability of denims related to cost. I've got multiple pairs of Tesco's "value" straight leg jeans that cost me £3 a pop in the mid-2000's. They are not much different in durability or comfort to my Levi's that were several times more expensive. The cheap ones get harder used if anything - as I avoid wearing the Levi's for doing anything that might mess them up.