I recently posted a blog about my experience w/ Cayston, which I would rate as 'not-so-positive.' I have not been back to my clinic yet for PFTs, but Cayston made me very short of breath. I was also nauseous/lost my appetite the 1st week or 2 on Cayston, then that went away - and it may not have been related to the Cayston at all, who knows.
The shortness of breath, however, I do feel was related, because went I finished Cayston I felt 110% better than when I was on it. Granted, this is just MY experience; it may work great for some people.
Price was not really too much of an issue for me, I qualified for assistance, so I paid $25 (or $28? something like that) for Cayston, and they also included the Altera, Nuk, soap & ziplock containers to clean them with.
I hate TOBI, but right now it seems like it is probably a better option for me than Cayston.