Chris,
Exploratory surgery for a diagnosis for arthritis? It sounds to me like your vet may be out to get your money My dog just had her arthritis confirmed by X-ray (she was under anaesthetic to have her teeth cleaned). We were quite sure she had arthritis because she limps sometimes, but since dogs (and cats too I think) won't sit still for an X-ray, they usually put them under anaesthetic.
My dog has been on Glucosamine and Chondriotin Sulfate for a number of years and it helps her. This may be something you might want to look into before exploratory surgery.