and how much would something like that cost?
Depends on the model. Those CD-1's you linked to are "middle of the road", cost you around $400-$500 new, ~$200 used. They aren't f'ed up, the horns were just cut down to fit in the install (perfectly fine as long as they didn't alter the actual throat). They are pretty good, supposed to have a good smooth top end
The 2nd auction you linked to are for CD-1E's, which are Image Dynamics "entry" level horns. Run you around $250 new and $150 or so used. Decent set, something to break yourself in on (when it comes to horns).
The last auction is for CD-2Comp's, Image Dynamic's top of the line horns. They appear to be on mini-horn bodies (smaller than full bodied horns). New will cost you around $850, used around $300. Now, those horn bodies do look f'ed up. Looks like the throat actually has a chunk missing out of it.
USD Audio also make horns.
http://www.usdaudio.com. They were the first guys to put horns in a car for car audio competitions:
http://www.usdaudio.com/sw/cars/buick/page2.php. I can't find the pic right now of Richard Clark holding the horns (RC bought that car and used it to go 26 & 0 in SQ competitions), but they were HUGE. Also believe they were one of the first, if not
the first, to use modified pro-audio equipment in a car. I also believe they were one of the first to utilize kickpanel mounting to minimize path-length difference......