I also have a dog which was recently diagosed with Cushings and she was put on Vetroyl, I'm not sure what you were prescribed, but the meds we have are 100.00 for the 60 mg through the vet and one pkg lasts only 15 days.. I agree this is pretty crazy at 200.00 a month as I can't afford that, but was forunate enough to find this same medication at Vetdepot.com for 64.00 a pkg.
I hope that helps.
Last winter we paid $100.00 for a ACTH stim test,$ 95.00 for a Cortisol test, and later $143.00 for a DEX suppression test. I'm not sure which test your referring to, and I'm sure prices are different everywhere. but if your in doubt, I definately would call other vets and ask.