I've been sewing disposable socks for 4 years now.
if you do not have a sewing machine, you can get a portable one for like $10-$15, good enough for sewing filter sock.
If you have a local Joann Fabric store, wait for their 70% off coupon, then buy a whole bolt (10 yards) for under $25 and that will make 180 4" socks. If you change weekly, that will last over 3 years. cost comes to no more than 25 cents per sock. and you get a brand new sock every week. you can never wash a dirty sock back to brand new clean, no matter how you do it.
if you sew your own, then you can control how much material you want to use, so there is no excess or unused portion before you throw it away.
I even make sock for 4" ring but the body is expanded another 6" so I have a bigger bag. I use this when I go out of town for over a week. otherwise, a regular 4" sock will start overflowing after 8 or 9 days. The larger bag can last two whole weeks.