One of the most peaceful places close to Bangkok for me is the resotel at kanchanaburi. Kanchanaburi itself attracts lots of tourists but the resotel built in the midst of the jungle next to the river is a nice quiet place to get away from it all. It does not costs a bomb as well
I just loved siting outside my lodging in the morning enjoying the cool air and listening to nature.
No street hawkers, no peddlers to ask you to buy something, nobody to ask if you want a taxi or a tuk tuk, few tourists but peaceful settings