In order to close a Thai company you will normally have to contact two government authorities. The first is the Revenue Department (RD) and the other is the Ministry of Commerce (MOC).
The Revenue Department
If you are a VAT registered company, you have to apply for VAT de-registration within 15 days of [...]

Labor matters are generally governed by the Labor Protection Act B.E. 2541 (1998) and the Civil and Commercial Code Section 575 to Section 586 on Hire of Services. Other laws include:

Labor Relations Act B.E. [...]

Here is a comprehensive document covering general costs, tax rates, labour costs, utility, communication, transportation costs, misc costs and useful information in fact everything you need to know when considering starting an operation or business in Thailand.
Download pdf document Thailand costs_doing_business_2009
Courtesy of www.thailaws.com