vet bills caused by our foster dog

We are here trying to raise money for a vet bill. One of my friends found a stray pit bull in a local park in Nashville and decided to take him in to see if she could find him a forever home with someone. One of her roommates ended up being allergic to the dog, so they couldn't keep him for long. I heard about this, so my boyfriend and I offered to take care of the dog until he found a new home, so that he wouldn’t have to go to the pound. We gave him the name Tank and bought him a few toys so that he could have some fun in the meantime while we shared to our family and friends about finding him a home. Tank is the sweetest pup and only wants lots of love and cuddles. He gets very excited when he meets new people. We knew that because he was a stray, his past traumas needed to be carefully considered. Unfortunately, we had an incident occur where Tank got out while someone was leaving the house. While he was running around the neighborhood, he saw a small dog, went after it and attacked it. We had never seen any signs of aggression from him before, so this was a tragic, scary, and surprising thing for us. We are completely understanding of the trauma that this must have caused on the injured dog. We were very apologetic and explained that we would do whatever we could to help resolve the situation and bring peace. The other family was not understanding or sympathetic of the fact that he was a stray and we were only an interim home for Tank. After a few days, the family sent us the invoice for their vet bill, which is what we are raising money for today. My boyfriend and I are both college students that are working and going to school full time. When we agreed to foster Tank, we did not have any idea that something like a $1,300 vet bill would be something that we would encounter. In an attempt to peacefully resolve this, we wrote a letter to the owners of the injured dog humbly asking for grace in the situation. Their response was harsh and unsympathetic. As a response, the owner shared that he was a lawyer, he would be taking this to the full extent of the law and grace was not in the equation. They threatened eviction, an animal control citation, and court if the check for the full amount was not delivered to their home within two days. Although we had no intention of being the owners of Tank, we love him, because he is truly a great dog. We want the best for him and we know that there is a family out there that would be the perfect fit. We wanted to do the right thing by taking in a dog that had difficulty finding a home and we never anticipated anything like this happening. If contributing financially is not something that is feasible for you, we would appreciate just sharing Tank's story in an attempt to find him a loving home.