Marcy, I'm sorry for your loss. I just went through a similar situation, and we're still puzzled as to why we lost our bird, who was literally fine one minute and dead the next.
If it's any consolation, I've had to just deal with the fact that sometimes they just die, you accept it and move on. Like you, I haven't seen any signs of illness. It's been a couple of weeks and everyone else is just fine.
You might consider giving a little plain yogurt as a probiotic. Make sure it's real yogurt and not the pudding-desserty type. Be careful not to over do it because it will cause diarrhea. The birds just love it.
I have VetRx. Sorry you were ripped off on the price. Your local Agway is usually a good resource for it for about $7. It does state on the box that it's for the prevention of disease and colds, but I'm at a loss on how it would be. Like speckled hen said, it's basically like Vicks for chickens, with camphor, balsam and rosemary in a corn oil base. I guess the FDA only covers medicinal claims for people, not poultry. Of couse I think a good stiff snifter full of sherry will cure a cold, but the FDA doesn't support that claim either.
I'm flummoxed as to how a state vet in GA wouldn't know about a necropsy on a bird. How do they test for avian flu, West Nile virus, and other highly contagious avian diseases? As Bugs Bunny would say, What a bunch of maroons..."
I hope the rest of your birds are okay.