Hello, we've got a 11 year old cat. He's never had health problems but recently he has started to throw up nearly all he eats. Sometimes it's instant, sometimes it happens several hours later. The vomit has a terrible smell. He drinks a bit more than usual, and urinates more than usual too. His urine also has a terrible smell. Pooing is very little (one little piece a day or two), he seems to struggle when he does it. His appetite is fine and even more. He's lost much weight and now is somewhat skiny. His behavior hasn't changed: still active, vocal and affectionate. Loves to be petted.
We have financial problems at the moment and it's unclear if we'll afford a vet bill. But how can we help our cat otherwise? Thanks
With the amount of water that he's drinking, It sounds like he's in the beginning stages of diabetes, as this is exactly what my cat did just before I took him to the vet. He's now on insulin for the rest of his life. However, by switching his diet to holistic foods, I have been able to reduce the amount of insulin he needs per dose.

So, given that your is a senior cat, the first thing I would try is switching him to canned holisitic food. It's far more easily digested than dry grocery store kibble. It doesn't contain all the fillers, grains and ash that contribute to or cause health issues. With any luck you may have caught it in time to prevent the need for insulin at all.