Staples Business Depot Binder Clips, Small 3/4″. 3/8″ Capacity black are on sale for $0.66 (regular price $4.97).
You can see this deal online here but since Staples charges for shipping you are much better off buying it from any brick and mortar Staples store in your area.
These binder clips will always come in handy and you can’t really go wrong for 66 cents!