My cat is sick, how can I treat him?

I have a 6 year old male runt. He has been throwing up a lot lately and he has a rat ulcer. He is very sensitive to cat food and will only tolerate a very specific package of cat food. But now even that is being thrown up. I would like to take him to a holistic vet but I do not have the money. I have a very limited budget of $50 for him and I would like to know if I can give him something that will help him. Natural remedies and such are what I am looking for.