Cortisone is an anti-itch and anti-inflamatory cream. I don't think it would be much help for a puncture wound.
When Aki was a kitten, he had a nasty abcess on his back that broke open. The vet suggested Neosporin or a triple antibiotic ointment. Both of these are painless and will help the healing process and to prevent infection.
I would not suggest using iodine, even if its diluted. Iodine can be used to disinfect wounds for many animals, but shouldn't be used on cats because they are very susceptible to iodine poisoning.
If the wound remains clean and uninfected, you should be able to treat it at home, but if it doesn't seem to be healing or becomes infected, then your friend will need to scrape together enough money to take the cat to a vet.