everything there is probably off the shelf except the mount.
if you are willing to do the leg work you can probably piece it together a couple hundred cheaper.
but they put it in a kit and cut hoses to length.
I did the classic kit and it cost me 50 bucks to get the hoses cut and crimped while I waited.

if you need a kit, then I am not sure if you are going to find it much cheaper.

As mentioned the other 2 big names are vintage air and classic auto air.