I went to immigration many years ago, as my visa was about to expire. I had a bad dose of food poisoning and told the IO., I was too ill to travel. She said she could give me a 15 day extension for 1,900 baht
Be careful, the Thai tax will be after your hard earned savings if you stay more than 179 days in Thailand in any year, 1st of January to 31 of December.
And still the billionaires and multi National companies will get away with paying little or no tax. As usual the ordinary guy/girls will be taxed to the hilt.