I know many have alread said it, but I'd like to reiterate that this group is SUCH a wonderful resource for those of us dealing with Cushings!
As far as a vet who won't write a prescription is concerned, have you actually spoken with the vet or just with his/her staff? I found that when I sat down with my vet and explained that I was working on a very tight budget, she would either 1) match local pharmacy prices on drugs, even though her retail price was higher, or 2) write a script on the condition that she periodically monitor the horse's condition via blood tests.
It's a valid concern of the vets that if they write you a script, that you'll disappear into the woodwork for a year or so, and adjust meds on your own. While you think this might help the animal, it could in fact be very detrimental.
My vet knows better than anyone that I am very sentimentally attached to my two useless geezer geldings. In fact, I work a second job just to support them, as they cost me thousands of dollars yearly. Being a horseperson, she doesn't ridicule me, but supports me in this decision.
Of course, she also knows that I'm a big believer in quality of life over quantity of life... when my guys deteriorate to the point where they're in pain, then it's time to say goodbye, however painful that may be.