How can I extend my Tourist Visa in Thailand due to a hospital stay?

The user is currently hospitalized in Chiang Mai and needs to extend their 60-day Tourist Visa to 90 days due to an injury. They have a doctor's letter for the extension but cannot go to immigration themselves. They are looking for an alternative to a high fee quoted by the hospital, which was 8000 Baht. Various commenters suggest different approaches, including getting a power of attorney to have someone apply on their behalf, discussing extension options with the hospital, and contacting a visa agency that may charge less.