The install, with gear, can vary quite a bit with gear prices. Maybe $6K for something like that including all the gear (can't remember exactly). But you could do something similar for half that, or double that. Lots of sound deadening in that Caddy, plus going in behind a terrible install. And all high end equipment.
When you get into custom fab work, suede, plexi & LED's, etc the price goes up. Same with the sound deadening, you can go basic or go all out, and the cost of material and labor to disassemble/reassemble the car and apply all the material varies quite a bit.
PROPERLY setting up and tuning an Audison BIT processor can take the better part of a day if you do it right. A lot of people know how to make it play, very few know how to tune the system to get your money's worth out of it.
Glad to see quality work like this still exists. I'm tempted to stop by and have you evaluate the wiring in my daily for the subwoofer amp. It's a basic install and a relatively low wattage deal, but seeing this makes me nervous, lol.