My cat Dusti had so many diseases (parents let him out, unneutered he was tomcat) he only lived to be 5 yrs old. Probably had FeLk and FIV and who knows what else. We literally woke up one morning to him dead. He had been suffering for some time and nobody did a damn thing about it. My parents suck. So I know the feeling!
Actually, I just sold some things last week to get money to take my bunny to the vet. Maybe if you have some things to sell that you don't use anymore or flyer your street offering to wash cars, windows or mow lawns you can raise some money to have your kitty checked out? :)