Not long since finished a three bed detached...one floor....all en suite .....large kitchen, diner, lounge......1.5 million baht.....plus another 0.5 million for kitchen, aircon, 1000 sq ft outside living space, Thai kitchen, 2m garden wall surrounding 0.5 rai.
Obviously price will vary tremendously re quality of materials, standard of work....but that gives you a rough idea.