Here is my two cents worth.
The dash of the NSX is obviously not something that can easily be modified. My installer is doing it with fibreglass and bondo so that he can flush mount a Pioneer Premier 940 (Which happens to play MP3s, CDs and Satelite radio). The piece will be custom painted before it goes back into the car.
You could also buy a dash piece that already has a DIN opening cut out. Either Dali or SOS used to sell these. They were something like 350 dollars though.
You have to look for the shop that can do the best work. Ask to see a picture book of installs they have done. If they have one, take a good look at the pictures, if they don't ask yourself why!!!! I know price is important, but would you shop around for the cheapest deal if you were going in to have triple bypass surgery?
More or less, if someone can get a deck into an NSX for $400.00 and it doesn't look hacked, you are getting a good deal.
Good luck