We saved a cat like that. Broken hip required surgery, 1 fang had to be removed, cyst removed, he was a mess. A little over 1 grand later and Hercules was ours for the next 8 years..
We had another cat called Polly that was sickly, turns out she had diabetes and the vet said "enjoy your time with her". We went to another vet who taught us how to inject her with insulin and she was with us for another 4 years. Every morning she would meet us at the fridge where she got a treat and we took out the insulin and jabbed her.
Ya gotta good heart Commander.