My idea of the day: re-usable cotton pads made from old t-shirts. I don’t know why I didn’t think of this earlier, as it’s so simple. All you need is an old t-shirt, scissors, string and a needle (or use your sawing machine).
Cut several circles (you can use one of your old cotton pads as a model) out of the old t-shirt and seal the edges with a few stitches. That’s all you have to do. If you don’t care too much about the look or you don’t mind that they don’t last forever, you can just cut the circles without sealing the edges. If you put moisturizer on them, they work very well as make-up remover pads. And they’re dirt cheap as well (old t-shirt=0 Euros). Put them in the wash with your other laundry and you can re-use them for a long, long time.