You could try these. Took about two hours to install using a 6" L bracket mounted to existing holes in the bottom of the hood. Needed to line them up, but they slide in right between the alternator and master cylinder.

Setup cost about $40. Wolo horns. Sound lot better / louder than stock. Not as good as I like, but wanted to check out the functionality in colder weather before getting something bigger. Last set I had would freeze up.

 

I used a Whelen electronic "air horn" that also has a public address mic. Super loud and easy install, although a bit pricey but quality stuff. All of the emergency vehicles use these.

 

I have the river raider evap/air tank skid. Easy to install, great simple product.