Unlike exotic vets, Betadine is neither expensive nor far away. You'll find it in the first-aid section of your local drugstore. That little bit of effort and expense will go a long way toward helping your snake pull through.
No sense in kicking yourself over your mistakes. We've all made them. Learn from them and move on. A neurological condition is challenging for even experienced keepers to handle. So, if you find you can't handle it, there is no shame in surrendering him to someone who can.
Bear in mind that "Betadine" is a brand name. The product is povidone iodine and you can find a bottle of the generic stuff for around $5 at a grocery store, drug store, Wal-Mart, etc. in the first aid section.