Three horns? Mine's only got two...
Things to remember - as disc-style horns age, they corrode and the vibrating surfaces get muffled, which changes the sound. Also, a bad ground will make the horn sound like a sick cow (and with - at least - two horns, the good one will keep you from realizing the other is bad).
Two aftermarket horns that I use and like - Hella SuperTones (two large metal RED horns; don't need a separate relay but comes with one so you can use it if desired) and Fiamms (forget which model, but they look like snail shells instead of discs and are also red, but plastic). The Fiamms are about $30/
pr, the Hellas maybe twice that.
The cool thing about the Hellas is that they're designed to p-r-o-j-e-c-t their sound. From near the car, they don't sound so loud. But move a couple carlengths out from the front, and they're VERY loud.
[RICHR]