Good luck with the rehab! Our rescue lab mix blew out a knee two winters ago while he was let out to go potty.. no idea what happened, but can only assume it was related to running/snow/ice/something.

Your quoted cost is right in line, I think he cost us about $3500 for the single knee.

Our dog has recovered exceptionally well and the other knee has never given us any issues, my understanding is that this surgery typically has fantastic results. Good luck!