Wow...it does suck when you pay all that money, only to have to put the pet down anyway, doesn't it?
We had a yorkie/silky terrier mix that my mom bought on the rebound when one of our cats died. She got it unknowingly from a puppymill. 2 days after we got him, he started throwing up and having diarrhea. We took him to the vet and they said he had cocciddia. (We didn't find out until the day we had to put him down that he REALLY had parvo. )
So here we are for 3 days, treating a dying puppy for cocciddia, for nothing.
We made 2 emergency trips to the vet in the middle of the night, and on the last time, it was for good. He was so far gone after all the many many tests they ran, that we decided to put him down - after $200 worth of vet bills. We got the money back from the breeder, but she refused to pay the vet bills.
So, not only did we have to go through heart-ache, major stress, sleepless nights, vet bills, having a very sick , miserable puppy, but we also had parvo in our house!!!!! We wound up buying tons of bleach and something called KennelSol to kill the parvo.
We wound up buying another PUREBRED Yorkie, and a Maltese at a later age then the puppy before, and with many parvo shots, they've never gotten parvo.
It's just a shame that vets have to charge so much, and often times run all kinds of tests for no reason. If I had allowed the vets to run all the tests for Misty's diarrhea, they would have probably done $100 worth of tests just for roundworms

That's why it's very important to find a good vet and talk to them before letting them run tests.
and again, I'm very sorry for your loss. It must have been hard