The price on the OFA's site is what they charge for screeing the films a veterinarinan takes. They won't vary from region to region. I think CERF is the same, and pennHip as well.
The variation in cost will come with the vet the dog sees. Many include the OFA's screening cost in their price and will send the films to the OFA for you. Your cousin might want to call around to local vets and see if any take OFA style x-rays.
The dog will need to be anaesthetized before having the x-rays, and will need to go to a vet who is familiar and experienced with taking OFA x-ray films. The accuracy of these films is crucial for screening. A bad x-ray can cause those screening to misread the x-ray and misdiagnose the dog's condition. Here is a great article on the importance of a good hip x-ray. http://www.leerburg.com/hipart.htm