Check under the thread Health and Nutrition and click on important health and nutrition articles and click on what to do if "I can't afford a vet", it will link you to AAHA, and other assistance programs. Also try typing in your search engine Pet assistance, and see what comes up. A company called petassistance.org help me find a low cost vet, A local shelter or vet can also give you some #'s if you ask for some. I did get info #'s from a vet that couldn't treat my cat. Don't give up it can be tiring and time consuming, but you have to call around. Try to find a low cost vet, the one I found cost 3x less than my current vet and I made a partial payment and he accepted a post dated check for the balance. Calling your local animal shelters and ask them for info for low cost vet/clinics would be a good place to start. Then just start calling around for different vets. You can also ask some of these assistance programs if they can't help you to give you #'s of who might, they have alot of info that can be passed on, but you have to ask and go looking for it.
There are a lot of grant programs, and even if you are eligable, they are very difficult to get and you need a vet who is willing to file all the paperwork, and most of these grants require a diagnosis first, so you have to go for an office visit and usually bloodtests too. AAHA has a good grant program at www.aahahelpingpets.org
but it is new so most of their vets don't know about it yet, so you would have to ask the vet if they are willing to file the paperwork, if so it will take 24-48 hours to approve, but it would be an option if the treatment of your cat gets expensive. But the fastest way to get treated would be finding a low cost vet that is willing to assist you with payments and will probably be the best option.
It is very important to get to a vet since it could be serious. I was just in your shoes last week, with no money and a very sick cat. He ended up having Pancreatitis, and if I waited it would have gotten worse and would have resulted in surgery, which would have cost more. Please don't give up on the different vets if asking for payment arrangements. Most of them will say no, but eventually you will find one, I called over 30 vets, then pet assistance called me gave me a # to a great low cost vet,(who was a better vet that my current one) He treated buddy, took a partial payment and accepted a post dated check.
I hope everything works out for you, I know how upsetting and hopeless you are feeling right now, but things will work out.