As a part of ASEAN, Thailand citizens are exempt from Vietnam visa for 30 days. For stay of longer than 30 days, Thai nationals may have 2 options: Visit Vietnam embassy in Thailand or apply for a visa on arrival to Vietnam from Thailand online. Thai citizens may apply for both tourist and business visa to Vietnam for the stay of 1 to 6 months from Thailand. Please check this link for visa fee for Thai citizens.
All the information for getting a visa from Vietnam embassy in Thailand can be found here: http://www.vietnamembassy-thailand.org/

Contact us at
+84 909-333-023
+84-9890-120-82