Red paint usually costs more because it is made up of more tints then other colors. Some of these tints can cost over $1k just for a quart. To mix the color you mix a predetermined amount of several different tints together. The tints used to make red are just more expensive. Its a total ripoff but all the paint companies are in it together (Dupont,PPG, Spies,ect.) when on raises their prices the others follow suit within a month or so.
As for the interior panels SEM make a great vinyl dye in an aerosol can its about $10 and you can get it at any auto paint supply store.