Chulalongkorn University lets anyone eat at their student canteens. Massive portions of real Thai food for ฿25-35. The som tam stall does proper Isaan style and the khao mun gai lady has a line of students for good reason.

Enter from Phayathai Road gate, canteen is in the main courtyard. Cash only, point at what you want if language is an issue. Eat where actual Bangkok students eat daily.