I found the following list on a website:
- 170 baht – average cost of a retirement visa, divided by 12 - for other visa types, note that this doesn't count in visa runs, business visas, school costs for education visas etc.
- 5,000 baht – Apartment (cheapest option, in buildings usually inhabited by Thais - the average cost for simple privately rented apartments is between 7,000 and 15,000 Baht per month for a small room of about 30-50m² in Pattaya or Chiang Mai, add 3 - 5,000 Baht for Bangkok)
- 1,400 baht – Electricity
- 150 baht – Water (sounded too low to me if you drink 2-3 l /day as you should in Thailand, I'd rather say around 400 B)
- 300 baht – Internet (mobile Internet package or occasional Internet cafe visits)
- 300 baht – Cable TV
- 200 baht – Phone
- 180 baht – Laundry
- 6,000 baht – Food (biggest possible range here, depending on food/dietary choices and scale of restaurants/self cooking - 6,000 Baht is the lowest possible cost when eating at markets, street food, or home cooking)
- 200 baht – Transportation (again: very cheap estimation imo - even when only using Baht busses or walking a lot, I'd estimate this with about 500+ Baht per month, not even occasional considering longer trips)
- 3,600 baht – Entertainment
- 1,000 baht – Other (like repairs, new clothes, shoes, cosmetic products, medication etc.)
Don't make the mistake to plan a long-term trip or permanent stay based on this number though. A road accident, health problem requiring a hospital visit, legal problems or drops in your home countries' currency rate etc. can lead to SERIOUS financial problems. Always make sure that you have good travel/health insurance valid for Thailand, and also a good bunch of money you could use if anything unexpected comes up - because many problems in Thailand you can indeed fix with money. Some of them you can only fix with enough money however…