My bird actually bit his sore foot off today.?

My bird got his foot tangled in his bed and it was bent back and really swollen. We took him to the vet and she gave us antibiotics and some stuff to put on his foot that smelled really bad. She also had us put him in a small cage where he couldn't move around. After the first day of treatments he started biting at his foot, we thought it was because he wanted to be outside with the other bird so we put him in his own cage during the day and kept a eye on him then after day 3 of treatment he was still biting at his foot so we stop putting it on there thinkning it was about the smell of the treatment. now it has been a week and he has bite his whole foot off. It was all black and now its gone. I really don't have the money to keep taking him to the vet. I banaged it up so that he won't bit at it anymore. What should i do?