Help! We rescued a baby RES, and we can't take him to a vet, we need a home remedy.. Can anyone help us?

Amanda You have written one of the BEST help questions that I have ever seen on answers. The shell damage sounds like the turtle was bitten by another turtle that was starving and trying to eat your turtle's foot. Your description of what you are doing sounds perfect. Melafix is good, I am old fashion and probably would have used Triple Sulfa, or Furan instead. If the turtle isn't too far gone your set up will allow it to heal as well as it can. I don't think that you need to take it to a vet. I have seen neglected turtles with bite injuries exactly like you have described. Thank You for your question. Your detail is fantastic. There may be hope for the world yet.