WELCOME TO THAILAND
Siam Real Estate & Siam Villa Rentals would like to welcome you to Thailand. We hope you and your family will really enjoy this wonderful opportunity to experience life in one of the most beautiful countries in the world. Whether you are moving here for retirement, spending time or working there are [...]

Working without a work permit is not something someone should take lightly as the penalties applicable are quite harsh.
Penalties applicable to the Foreign Employee
A foreign citizen who:
-          is working without a work permit or
-          doing work other than that specified into the work permit
Is punishable by a fine of 5,000 THB + 3 months of [...]

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

When do you need a work permit?
You will need a work permit as soon as you engage in work by “exerting energy or using knowledge whether or not in consideration of wages or other benefits “. Of course if you just come into Thailand to negotiate a contract with a Thai [...]

First, you must have a Non-Immigrant visa to apply for a work permit.
With a few exceptions, all foreigners engaged in any kind of work in Thailand must hold a valid work permit. These are issued by the Department of Employment, part of the Ministry of Labour and Social Welfare.
The term “work” [...]