For most dogs over about 15kg with a full cruciate rupture, surgery is the recommendation a specialist would make for their own dog: without stabilisation the knee stays painful and arthritis accelerates. For small dogs, partial tears, and dogs with serious other health problems, non surgical management is a legitimate conversation.
Send what your vet said and quoted. A veterinary surgeon reads it and comes back to you with what they can do and what it would cost, before you pay anything. A written second opinion is from $250.
Conservative management is not doing nothing. Done properly it means eight or more weeks of genuine confinement, weight loss where needed, anti inflammatories and structured physiotherapy. Done half heartedly it is just a slower route to a worse knee.
Braces and supplements are heavily marketed to owners in exactly your position. Evidence for custom stifle braces is limited; evidence for supplements alone fixing a ruptured ligament is nil. Be careful spending surgery money on non surgery.
Send the case, hear back from a surgeon with what they can do and what it costs, and only pay if you go ahead.
A ruptured cruciate does not regrow. Reduced limping usually means inflammation has settled and muscles are compensating, and the limp typically returns after exercise. Improvement is real and worth noting, but it is not the same as a healed knee.
A dog that sits with one leg kicked out to the side is showing a classic sign of knee discomfort, and vets do weigh it. But diagnosis rests on the examination, drawer and thrust tests, and x-rays. One sign alone should not settle a $6,000 decision.
Many experienced vets can be confident on examination alone, but imaging confirms the diagnosis, rules out surprises and sets a baseline. It is completely reasonable to ask for x-rays before committing, or to ask an independent surgeon to review what has been done.