Save the grey tabby

I opened my front door today to find this grey tabby right at my door step.  He was so weak that I thought he was paralized.  It was extremely easy to pick him up.  I saw he was suffereing and injured, so I took him to the vet.  After some tests were done, it turned out that he tested possitive for FIV, but negative for leukima.  After more tests his blood work looked really good.  The kitty is suffering from an infected tail.  The doctor was confident this kitty has plenty of years left to live, just as a bob tailed cat.  The vet said if I saved him, at least he would not charge me for nueturing him.  

I do not have it in me to end a life, when I know there is a good chance of survival.  I just mentially can not make that choice.  I am scared and stressed about how I am going to pay for this, but I rather be financially stressed then to feel guilt for not saving a life.  If I were found on the side of the road, they would do whatever it takes to save me.  This kitty as a fighting chance..    PLEASE HELP!