I'm so sorry to hear this. My senior cat Storm is now 14 1/2 years old and last year in Oct. he also started vomiting almost daily. It turned out that he has small intestional disease which I guess is a form of IBD. He's been taking prednisolone and now takes 2.5mg every morning. I also give him 5mg of pepcid at night which is 1/2 of a pill. Since you've changed his diet it could also be the food. Try to see if any vet will accept payments. Lots of prayers and positive thoughts are being sent his way.