Stayed in Bangkok with my fiance for a week and on day 3 overheard someone talking about pier 21. It is on the 5th floor of the terminal 21 mall(on skytrain at Station Asok) you just go get a card at the front or back kiosk and fill it with a much money as you want then you visit any of the food stalls and buy very cheap food in a clean environment. They have all the classic Thai dishes. Dishes are a bit on the small side but on the other hand for 60-70 baht you get to try 2 different dishes versus a single dish if you were to buy street food. We kept coming back for super for the next 3 days after discovering it. They also have great fruit smoothies for cheaper than anywhere we've seen in Bangkok. My fiance loved the papaya and mango salad. Just see where the lines are longer and you'll know what's best!