I think it is about right. 40K THB to be well feed, even have a couple of beers a day. We have no rent, our own new condo (that was 70,000 AUS dollars) back in 2008. Bang Na, someting like Bondi Junction in Sydney,
Around, there are hospitals, companies and condos, maybe 20,000 people live within that realm, there, a whole cottage industry of Thai food along the street. No way you can cook better or cheaper (and no smell in your house) yourself.
My wife would go out, and, along with professional office women, buy the same food they (the professionals, in designer atires) take into their BMWs, Mercedeses and take home.
I can tell you why you are, as a single woman, as safe as in a kinder garden, in Thai. But the Mods would not let my answer go through. There is a fundamental reason why you will be safe in Thai, as a single woman.