I worked in BKK since 2016 and office staff usually goes to the cheapo restaurants (which I frequented too), so 40-80 baht is completely common also for white collar workers. But meat, vegetable and oil quality is really shady in that price range.

I prefer to order grab of around 120-200 baht from a "healthy" place or going for restaurants within Central 200-400 baht per meal.

(including drink) .. if you eat rice something with water everyday, it's quite a tight lifestyle.

I love the tightest lifestyle eating rice and 1-2 side dishes from street vendors who deserve the money rather than foreign investors to extract money from the economy like leeches.