As I read your post you seem to be asking how much would the price difference be if you want to do a 2-tone paint scheme... Since most of the cost of a good paintjob is in the prep work that should be the same if you paint it a single color or two-tone, their will be some additional labor to mask and base the second color and the clearing process should be about the same. I think it would be reasonable to expect the two tone to cost somewhere between 10-20% more than a single color. As has been said before, cost will depend greatly on who is painting it.

Here is something you might want to consider... Many paint shops prefer to spray "their" brand of paint and will charge more if you insist on a certain brand. In some cases like some of the House of Color paints you have no option but to spray their color as they are impossible to mix, but since you are looking at factory colors the paint formulas are readily available. In my shop if you insist on PPG I am going to have to charge more since that is not a brand I spry often and therefor don't keep their products in stock or buy them in bulk.

Dave Brisco