My lab tore her ACL when she was 4. Same thing, vet said it would cost $3,700. I was also told that after the surgery was done, I'd have to keep my dog pretty much immobile for I think it was 4 or 6 weeks. I'm not sure what kind of temperament your dog has, but my lab was high strung and ready to go. I knew that keeping her calm wasn't going to happen. The vet said it will eventually "heal" over time, but I still had to keep her on the calm side. I went that route knowing I would literally be blowing almost 4K with surgery. She is 11 now and runs fine and moves fine with no side effects. Surgery is probably the way to go, but there are other options. Hope your pup recovers fully either way.