What documents and fees are needed to extend a 30-day visa exemption in Thailand for dental treatment?

Extend 30 day Exempt: My brother-in-law (Australian Passport, and over 50 yrs old) has been staying here in BKK for the past 28 days on a visa exempt 30 day entry. He has been getting some major dental work done on his teeth whilst here (which is continuing) and now realised he will be unable to depart Thailand on the 30th day of his stay (tomorrow) due to the ongoing dental work taking longer than initially planned. It seems he either needs an extension of up to 1 week, or incur over an overstay, or border run (not a convenient option). Since he will need to return to Thailand in another 3 months for another session with the dentist I advised against incurring the overstay. Therefore, if I take him to CW to apply for the extension tomorrow, what documents does he need to provide to the IO and how much is the fee?