A quality paint job is only as good as the prep stage. You must spend the time initially to sand, prime, and seal the piece before any of the custom work begins, that prep work takes time and material, this is why all custom painters have a starting price; to get to that clean slate stage.
Custom painting is just that, custom, and every finished piece will be unique to the owner. If you wanted the same 'eagle with flaming skulls' helmet as everyone else, you'd just get a helmet off the rack and be done with it. The average starting price for a helmet or mask is around the $500 mark, and roughly $1200 for basic (3 piece) motorcycle paint, but feel free to give me a shout with any questions so you understand exactly what those costs do and do not include.