Since August 2014 it is not possible anymore to stay for a long term in Thailand without a visa. When entering Thailand without a visa, visitors from 46 countries will get a stamp in their passport which allows them to stay for 30 days in Thailand.
This 30 days “temporary permission to stay” may be extended for another 30 days only once at any local Immigration office for the cost of 1900 Baht.
Extension up to 60 Days Total
For this extension on the visa-exempt stamp you need to provide:
- Onward ticket (out of Thailand) within the next 30 days
- 1900 Baht application fee
- 20,000 Baht per person to show that you can afford to stay in Thailand
- Hotel booking confirmation
- 1 photo (passport size)
So you can only stay for up to 60 days in Thailand without a visa (30 days 1st entry + 30 days extension).
A way to further extend your stay in Thailand is a Visa Run to a neigboring country to get a Tourist Visa with only one entry, which is good for another 60 days. Tourist Visas with multiple entries and a validity of 18o days are only issued in the visitors home coutry.