I hate to be direct, but if you can't afford vet care, you can't afford the snake.
Get that guy to the vet asap. Use diluted betadine to sterilize and clean the wound.
And feeding large rats to ball pythons is a no no. Most would be medium. Feed smaller and more frequent meals to avoid feeding large and less often. Live large rats are highly dangerous.
I feed all my adults small rats weekly. And to my big girls, a couple small rats in one shot.
Sent from my DROID RAZR using Tapatalk 2