Cheap places to go in bangkok?

currently in bangkok and need to do some things trying to budget as much here untill we go to phuket next week, we have been tiger temple grand palace many other palaces and floating market waterpark but now we have to budget our next 4 days here , we are finding food to be around 200bht per person for a plate of rice or something is there somewhere safe close to silom rd to eat cheap, and somewhere near sirlom road (narai)hotel to do washing,