Originally Posted by evilfij
Discovery horns are pretty close and should be cheap to free used. Warning those horns are WAY louder than they seem in the car. Not suitable for a kids toy.
You can also stuff the outlet of the horn with foam or spray foam it completely shut and drill a hole bigger and bigger until its loud enough for effect but won't hurt anyone's ears. We did this to a siren speaker on a gator used in large crowds. Worked like a charm.