From Chris in Canada:
Need cobwebs or spider webs for a scene? Check out your garage, shed or (blush) the pipes coming
into your basement laundry or furnace room.
Give them several mistings (3 or 4 should do it) of cheap extra hold hair spray. When dry,
remove the reinforced web carefully and lay flat on waxed paper until required.
Technically speaking they aren't trash, nor are they trash in the opinion of their creators,