ray1966, are you looking for sit down restaurants? If you also consider takeout then there are ekiben (駅弁) it is boxed meal sold at train stations. Ekiben was used to be meal passengers on long haul trains bought during the journey. So Ekiben is usually sold at station where long distance train depart and arrive, such as Tokyo station, Ueno station, Shinjuku station, and Shinagawa station. Other stations my sell but those stations will sell and often has variety of selections. Chopsticks will come with ekiben, also bottled drinks are sold so you can have a meal at your hotel room if you do takeout. Price of ekiben is usually around JPY 500-1500 and up.

Another takeout options are convenient stores. Convenience stores in Japan sell a lot of boxed meal (弁当) along with other items which is very popular among single salary men in Japan. I will show example for Seven Eleven stores in Japan, it is very popular convenience store in Japan, website is in Japanese only but you get ideal by looking at pictures.

Obento sold at Seven Eleven, from going top to left to right:
Korean beef BBQ over rice (JPY 489)
Korean pork BBQ over rice (JPY 398)
Fried rice with char siu (Chinese roast pork) (JPY 398)
Makunouchi bento, most common boxed meal in Japan (JPY 398)
Deluxe makunouchi bento (JPY 500)
Japanese style hamburger, fried hamburger patty with soy sauce flavored demi glace sauce (JPY 500)

Zosai, Japanese single dish items:
Edamame (JPY 158)
Soramame, looks like similar to lima beans but it is green on color. (JPY 158)
Vegetable cooked on soy sauce flavored broth (JPY 250)
Eggplant with miso/meat sauce (JPY 198)
Fried shrimp with mayonnaise (JPY 398)
Japanese style Salisbury hamburger stake (JPY 250)
Chinese dumplings, pork (JPY 230)
Chinese mapo tofu, pork (JPY 250)
Stir fried liver and leek (JPY 298)
Goya-champul, Okinawa stir fried dish with slightly bitter pickling melon (JPY 280)
Fried chicken skin, two types shown on the website (JPY 230)
Cooked spinach and sesame seeds (JPY 198)
Cucumber and seaweed sunomono (vinegar rice) (JPY 170)
Cold tofu with soy sauce (JPY 138)
Salad (JPY 280)
Chicken steak with garlic pepper (JPY 398)
Sautéed pork with garlic (JPY 350)
Cooked spinach with half boiled egg (JPY 298)

Oden, fish cakes and vegetable slow cooked in soy sauce flavored broth, as you can see on the picture at the website. You pick what you want most of them are JPY 100 each.

Also, family restaurants like Denny’s also have Japanese items which is also good cheap eat and family restaurants are everywhere in Japan.

I am really getting hungry.