... but its not really our cat. It kind of just adopted us.

Its a stray cat, which our elderly neighbour used to feed. Then she died. The cat then came to us as no one in the neighbourhood otherwise looked in its direction. That was over a year ago now.

S/he was very timid and scared of humans at first but has grown in confidence around us, to the point it will rub itself on our legs and drool (so gross!)

Anyway, the cat eats, both what we give him and what he catches. Only it doesn't gain weight. As in if you run your hand down its back you can feel its spine and ribs very clearly. I don't remember it ever being this underwieght before.

It will eat now and then vomit every so often, so isnt getting a full meal all the time. It has food and water available to it all the time.

Whats wrong with our not-so-ours cat?

Im a bit worried about taking him to the vet as I;m worried that it will be a one way trip either because of the complexity or cost Any ideas what we would be looking at in that regard? He has always come and gone as he pleases, mostly now he doesnt venture far from our back door. I have no idea as to age either.