My puppy Gunner's battle with Parvo

Hi everyone,

As most of you know, I was very excited yesterday to pick up my new puppy from the rescue group Caring Canine Connections of Bridgewater to help me with my anxiety and improve my overall quality of life. After driving over an hour to the foster home at which he was being held, I got to bring home the precious boy we now refer to as Gunner, a german shepherd mix.
Initially, Gunner was sleepy in the car, which I wrote off as puppy exhaustion. Towards the end of the ride, he vomited, which I wrote off as car sickness. After a long night and many attempts, Gunner would not do much other than lay on his new bed. He would not eat anything, from his food to chicken breast. At this point, I had assumed that he was just shocked at the change in his surroundings, and did my best to make him comfortable. In the morning, Gunner was not interested in breakfast. At this time I reached out to his foster mom and asked her for the food he was eating while he was in her care. He showed no interest in that either. It was at this point that Gunner started vomiting and having diarrhea despite not having anything in his system. He was extremely lethargic, and while everyone was telling me it was just his adjustment period and nerves, my intuition told me otherwise. Tonight, I took him to NorthStar Emergency Animal Hospital in Robbinsville where he was tested for ParvoVirus, a highly contagious viral illness among canines that deteriorates their gastrointestional and digestive system, causing all of the symptoms that my new pup had rapidly developed over the 24 hours I had him.
The SNAP test (used to test for Parvo) came back as a strong positive, and I was told that treatment would have to start immediately and would reach upwards of $3400, or he could be returned to the rescue for a refund and would likely be euthanized. I opted to have them begin treatment, which has an 80% success rate as inpatient, and under 50% success rate for out patient. I have received an "unfit for sale" letter from my vet for the rescue stating that they are obligated to reimburse me for double what I paid for Gunner (which was $380) in order to help with medical expenses. I have been receiving phone calls from the rescue in which they state to take my dog and leave the vet because the vet is "lying" and trying to take my money, and they will take Gunner to get fixed at their vet, which I can only assume is so that they do not become financially responsible and run the risk of losing their reputation. This situation has all happened in under 24 hours, and I am not exactly sure where to go from here, so I'm reaching out to anyone who may be able to spare any fund to help get my boy the care he needs to overcome this destructive virus. Any help is appreciated and updates on his progress will be made daily. Thank you for reading and thank you for your help. Gunner and I appreciate it and hope we can get him back home to start making memories together soon.