Help save a cat's life!

I found this sweet tabby boy (I've named Doctor; Doc for short) in my yard Sunday, 2/25/2018. His foot was infected and he had no toes! I've taken him to the vet and the vet said it was most likely an animal bite that became infected, so much so that the toes rotted and fell off. This will not heal on its own and his leg needs to be amputated. I've gotten a quote from the vet and am taking him for a second opinion as soon as possible. Doc will not survive if the leg is not amputated. His leg will continue to get infected, and fall off.

This is from my original Facebook posts: 
(3/1/2018)UPDATE!!: Doc was sedated this morning, checked out, and he's clean!! No FIV or FeLV! I will be taking him to get a second opinion to see what another vet says. That being said, should the SPCA be the cheaper option, the vet said there are medical students coming to watch him perform surgeries. If I could postpone until then, it would knock "about $100-$200 off the bill". Which would be fantastic. I will set up a GoFundMe tonight to start raising money for the amputation. The vet says he will be a permanent indoor kitty, as he will not be able to defend himself or run fast enough outside. He received his rabies shot today, as well. Even though Doc is skinny, he's a whopping 15 pounds and estimated at about 12 months old. So he's going to get bigger. ‍♀️

(2/28/2018)So, I took the stray I found Sunday (Doc) to the vet today. The loud doggies in there scared him, so he wouldn't let anyone touch him to be examined. So I'm taking him back in the morning and he'll be sedated and have his blood tested/foot examined.

About his foot:
From what the vet told me, Doc was bitten by another animal several months ago and the wound got so infected that his foot and toes fell off. The wound will never heal and his leg will continue to rot and fall off, no matter how much I clean it and take care of it. He will need a full leg amputation, which is shown at a whopping $853. Not bad, considering it's major surgery, but that's not something I can just pull from my backside.
I find out tomorrow what his test results for FIV and FELV are. If they're positive, the most humane thing to do would be to help see him off over the Rainbow Bridge. If his results come back negative, he'll be put on antibiotics and scheduled to be neutered. An amazing woman is helping me through a local rescue, but to ask something that grand of a scale isn't a thing I'm going to do. That being said, I will set up a GoFundMe for his surgery.

I will post another update as soon as possible. Please share and get the word out. I'm hoping to be able to give this poor soul a second shot at life. Every life is worth it. To not try would be to throw an innocent life away.