I agree $30,000 is at the high end, but you can't just say all paint jobs are the same except for price.

Is it painted in side and out, top to bottom?

Did the guy want show quality? (it is different)

I doubt if they used "decals" on a nice custom. No doubt the graphics are painted on.

What condition was the bodywork in?

Did they have to make body modifications to make it authentic.

Who did the work? (famous people often charge more...because they can!)

Here in Tucson, a good solid color repaint requires a minimum of $1500 in materials, and a minimum of $3500 in labor. It goes up from there, depending on many, many things.