Need help affording care for my stray cat

This is my friend Mister. He is a stray cat that has been showing up at my door for a couple months now. He came to me the other day with what seems to be a broken leg. I tried calling animal control but they couldnt help me beacuse i fed him for more than 48 hours and so legally he is my cat now. I have been to a couple of vets and they gave me a really high price for treatment. I waited a day or so but it breaks my heart to see him limping around and cant defend or help himself. I am a full time student so i cant possibly afford treatment for him. Anything will help I want to give this poor guy the help he deserves