Carried my motorcycle battery into a junkyard and walked around blasting horns on old Cadillacs, Buicks, etc. Ended up with a dual set off of an old full size Ford van. It was $5 per horn, so $10. Some of those old car horns are pretty loud- I'm happy.
that's exactly what I was going to post!! I went to a local auto salvage yard (aka. junk yard) and got some horns for $5 for the pair off of an old chevy van. you can easily mount 'em under the cycle near the kick stand area of the swing arm.