An MRI will solve nothing, if the vet doesnt know what they are looking at. In the long run it is always cheaper to have the correct diagnosis, then throw darts. With 1000 invested you should have had at least an answer as to why, what it will take to fix is another story. In the 30 years I have had my same vet, I have never not had a why something is what it is, within a day or two at the most. Most times its within the hour.