Unless your going to do your mustang in Kameleon, 4500 for materials sounds pretty steep. As a distributor for House of Kolor, I can tell you first hand that HOK has a bad rap for being expensive... One of the main reasons for this is, most distributors/shops tend to mark up everything that has HOK written on it.
When you decide to do the job, I would find out everything you need for the particular job, and shop around. It is also very important to make sure that if you start a job with HOK, you should finish with it. I cant tell you how many Kandy jobs have come back and the color has been bleached out only after a coulple of years of being out in the sun....
The reason for this?
There are painters out there who will sell a custom job and say they use all HOK, but they will cut a corner and use lets say PPG, or w/e clear. The problem with that is other clearcoats dont have the UV protection that HOK clears have. The best part about it is that HOK clear is fairly competetively priced to other quality clearcoats on the maket.
And to answer the question of weather use should consider using HOK or something else on a custom job, i belive that there is no contest. While Dupont has recently tired to come out with "Hot Hues" and BASF has their own custom line, none of them have the clarity that HOK offers. Having talked to the founder of HOK, Jon Kosmoski many times, he has indicated that the other companies are merely immitators focused on trying to enter a hot market, while HOK has and is the innovator in Custom colors since 1956.
In the end the choice is yours but if you want a show winner car, I would make sure you have a competent painter, and shop your materials, and consider buying them first hand so you know what is going on your car
There are many "HOK" jobs out there, that arent HOK....