My cat began to vomit saliva and water and then a yellow stomach vile?

She's strictly an indoor cat, 4 years of age. I do not have any plants and I've never known her to get into or eat anything odd. She basically doesn't like people food, just her dry food (excellent quality). I have 2 other cats who eat the same food and are fine, so I've ruled out the food being tainted. I took her to a vet, had x-rays, she hadn’t swallowed anything, intestines, liver, kidneys looked fine. The vet gave her an injection of fluid to flush her liver and kidneys. Two days later she's still lethargic, and refuses to eat or drink. I tried force-feeding and she thew that up. I've been out of work for over two years and the vet visist cost $189. I can't afford to spend another $100 on a blood test. I saw where someone wrote if you a person can't afford a vet visit they can't afford a cat. (What, should people throw out their pets out and put our children up for adoption if one loses their job?) I'm at a loss and bothered that the vet I took her to knows my situation and simply won't advise me of what I should or could do. Suggestions? I'm requesting that suggestions not include making calls to shelters to beg for help. Again, I repeat, I’m requesting that responses not lecture me to make calls and beg for help. Thank you.