I am so very sorry for your loss!
Yes parvo is highly conatgious and the number one killer of puppies and alot of people really do not realize just how important it is to take precautions.
I will say that it IS possible that he picked it up from the Vets office. I have heard of this before and from my understanding there are a few articles out there that even say that it is airborne? Also if the vets office didnt not clean their floors, table or scales after an infected dog was in the office then it could easily be contracted that way as well

Hopefully your breeder will be honest with you and let you know if any other puppies were sick so you will know.
As for the vets office. I have heard that dogs can be diagnosed wrong for Parvo as the test will show up positive once a dog has had the first vaccine. That is just something else to think aobut.
$8000.00 sounds very steep to me. In my area it cost upwards to $2000.00 to treat it and no guarantees.
Also please keep in mind that you would have to bleach your home and yard thoroughly and it still may not kill all of the infectious bacteria. I have heard that you should not get another puppy for 6 months to a year. If you dont want to wait and want to fill the void now then maybe you could rescue an older chi that needs a home. Just make sure that they have had the full series of vaccines