Clint, I recently installed a kit from HORNBLASTERS.COM.
You can buy entire kits from their website, and on eBay as well. I got mine on eBay, because they had a "Buy It Now or Make An Offer" option.
The complete kit I bought on eBay was listed for $549.99. It's called the Shocker S4 kit.
Using the "Make an Offer" option, I actually got it for $459.00.
Shipping took about 2 weeks, because the solenoid valve was on backorder. The guys at HORNBLASTERS.COM were really easy to work with, despite the minor delay in shipping.
Go on YouTube and type in Hornblasters. There's PLENTY of videos of people blasting their horns and scaring people!
After seeing these videos, I HAD to have a set.
I did a really clean install, I put pics in my gallery if you want to see them. The whole job took about 8 hours. I mounted the tank and compressor on a steel plate, and mounted it to my rocker panels, along the frame rails. Ran the wires into my ignition switch, and to the battery. DEFINITELY use a in-line fuse near the battery, just in case.
Also, as mentioned above, plan on dropping a pretty penny if you want BIG sound.
I love my horns. So do other people
It's WELL worth the time and money invested.
If you have any questions, holla at me.