Severe Itchy Scalp HElP! Please?

I am bothered by severe itchy scalp. I have seen a dermatologist without any real help. He wrote a prescription for "medicated Shampoo" but it cost almost $400.00 a bottle so it is not an option. Both the doctor and my hairdresser agree that there is nothing visibly wrong with my scalp. It is not overly dry or overly oily, no dandruff or any other conditions. I have tried rinsing with a baking soda solution, with moderate success. I am now trying a vinegar rinse but it is too early to tell. I do seem to get immediate, though temporary relief. That relief may or may not last... too soon to tell. Any thoughts would be helpful. Thanks