From THAILAND IMMIGRATION ACT, B.E. 2522 (1979)
Rate of fees, working fees, and other expenses (Page 38)
(3) Application for extension of temporary stay in the Kingdom under Section 35, per person, each time 2,000 baht
Unofficial translation http://web.krisdika.go.th/data/outsitedata/outsite21/file/Immigration_Act_B.E._2522.pdf