I found Betadine for the cheapest at my local Walmart--about $10.00. Everywhere else it was $14.00 or more, and you can find it for that price at Rite Aid, Walgreens, Fred Meyers, etc. any local grocery store with a pharmacy aisle.
If you do purchase Betadine, make sure it is a 10% solution. Put the snake in a tub and fill it with room temp water, about 3/4 the height of the snake, and wait a minute. They usually like to drink the water.
Then add some betadine. Wash your hands with sanitizer and mix the betadine with the water, adding more until it looks like an iced tea color--a light brown. The stuff smells pretty strong so make sure there's good ventilation in the tub. I just put my hands in and gently push my hands so the mixture washes over the parts of the snake that are affected (they usually try to slither out of the tub, and don't soak the affected areas). I let them crawl on me so they don't feel trapped, and gently wet my hands with the mixture in the tub and then rub it over the snake.
This is just what worked for me. My snake is looking a lot better.Good luck!