As khunPer states, it is all about location.
I bought land more than 20 years ago for 3 million baht per rai. My friends told me that I was stupid as most land on Samui was 1.5 million or less. There was no electricity or water and just a dirt track to the whole peninsular.
About six years ago I sold one house and some land. The going rate then was 35 million per rai.
Sorry, no idea about prices now.