I bought mine at a sailing shop too.
About $15 a piece except for the 3rd one which has a Becket which allows you to attach a Caribiner to clip pack hauling loop too.

Having a bearing of some type makes all the difference as well. Some cheap ''clothes line pulleys'' are just metal wheels on a metal shaft.
Under a heavy food pack load the friction is noticable.
With a good pulley system you don't need to "haul' your pack up hand over hand, you just walk the line out and it's effortless, even a little kid could do it. ;)