Cheapest of all. Poly sheeting ('Visqueen', etc.), 6 mil. Make a pillow from it using duct tape, 2 or 3 layers. Stuff firmly with wads of same. Stuff the whole thing in a burlap bag, stitched closed with nylon cable ties. Hang it from the corners between two fenceposts with rope and bungees.
Stops anything. Don't use with broadheads--it stops them easily but they are difficult to remove and the broadheads cut up the burlap.
It will work fine without the burlap bag if you are in a hurry. Fashion hanging loops on the corners from duct tape. But it will eventually leave a mess.
It will last for years if protected from UV by the burlap (also use UV resistant cable ties--usually black colored). The burlap also keeps deer and birds from picking it apart. When the burlap gets shot out, just remove it from the old bag and stuff it into a new one.