Unfortunately Jenn you will find that most of us in the same position as you find yourself in. If I were to add up the cost of the medication I've had for IIH for the past 22 years, I would probably find it would be astounding, not to mention the added medications for pain.
As an ex NHS employee I've learned that it all comes down to budgets, postcodes, politics and government policies. This sadly is the cornerstone on which the NHS is run, and because of this there are many people with serious conditions who don't benefit from free medication. I am sure it has also alot to do with the drug companies because one hand greases the other.