Cheap food doe not have to be unhealthy. And service at cheap restaurants does not have to be unpleasant. Tokyo is full of restaurants optimised to be cheap and fast while serving good quality hot meals in a clean restaurant with great customer service.
Commonly you will order your meal in a vending machine and get a ticket in exchange. The waiter will place a glass of water in the desired seat for you, you hand will hand your ticket to the waiter, receive your meal in exchanged and leave shortly after completing it. These fast style restaurants usually serve udon, ramen, rice dishes, with eggs, vegetables, pork, beef, curry. All these dishes cost less than a Starbucks beverage.