A good expat salary in Koh Samui depends on an individual's lifestyle and needs. Generally, a monthly income of 50,000 to 100,000 THB ($1,600 - $3,200) is considered comfortable for a moderate lifestyle, including rent, utilities, groceries, and entertainment. However, those seeking luxury living may require a higher salary. It's essential to research and consider personal living expenses to determine the appropriate salary for your desired lifestyle on this beautiful island.