Is there another vet you could get a 2nd opinion from? You have already had x-rays done so they should be able to review those which would save some cost. Maybe ask about financing/care credit etc. If he is losing weight and definately not acting himself he probably needs medical attention. From what I understand, by the time a cat starts to show discomfort they are already pretty bad off--cats are masters of hiding their discomfort. Sorry I don't have any better advice.