I think a person could do fine on 40K. After all you can live rather cheap here if you have a mind to.
Thai people manage on much less.
A simple room without a/c can be found for 2k a month. A person can eat for less than 100baht a day. Say another 100 baht a day for transportation and laundry, 2k for miscellaneous shit adds up to 10K, leaving you 30K in the bank. You'd be living like a monk but worse things could happen. Like blowing all your hard earned money of booze and women and slithering back to your home country broke, nursing a bad liver.
The key is having an mind to.
I know a fellow who can here with nothing, taught english in BKK for a while saved his pennies and later opened a nice burger place in Pai. If you don't believe me talk to Ed at the burger place in Pai. He's doing well for himself.