Hmmm well after googling Thermal Straightening, im guessing that is the procedure I have done with mine.
I have it done approx once every six month period and have it done at Servilles. (Ive been having my hair straightened for about four years) and I had to have a test patch done before they would do it the first time. My friend (who is a hairdresser at Servilles), cut some of the hair from the back of my head and took it in to the salon to test it for me as you cant have too many chemicals in it (such as when you dye your hair blonde, my friend couldnt have it done as the hair "melted")
It literally takes hours! The price also depends on the length of the hair, my hair is usually just to the bottom of my shoulder blades, the shortest my hair has been is shoulder length. It costs me $350-400, but I figure I only get it done twice a year and dont have really any other hair costs so it works out relatively "cheap"
I love the way my hair feels so soft and silky after having it done (and the way I never have to do anything to it, basically wash and leave) if I want it to be really soft and shiny I just run the GHDs through it. Oh and my hair is naturally very curly, think a baby sheep