I'm very sorry, OP. I love my cats and consider them part of the family.
I do think, though, that if you cannot afford all available testing and treatment, it is selfish not to euthanize. Either provide the best medical care available or allow your kitty to die peacefully (preferably at home: please find a vet that will come to your house so your kitty can have a peaceful end in the comfort and security of her home).