Matsuya is an extremely well known chain budget restaurant that usually serves beef and rice at 250YEN which is a good find. They also have curry, kimichi and pork with rice and several set meals that are less than 1000YEN. Matsuya is 24 hours and also serves breakfast.
While Yoshinoya are much more popular for the tastier beef and rice bowls, they also serve a variety of other types of meals that come in different sizes- Small, medium and large. Yoshinoya also has deep fried foods like tonkatsu and fried ebi among others like teriyaki chicken and curry rice.
Yayoi Ken serves mostly set meals under 1200YEN and are very popular for their rice-refills. This means, you can refill your rice as many times as you want and get your worth for your money. Most set meals are under 1000YEN and are quite huge in portion. They have a huge variety in their menu that comes with fish, chicken, beef and pork. It is certainly a good find for a hungry man. Please also do note that refilling of rice is self-service.
Suki-Ya is another popular eatery for Gyu-don (beef and rice bowl) and also offers different sizes for their meals. Albeit the same as Yoshinoya, they are known to be give their value for your money and usually have sit-in booth areas instead of the usual table at the counter type. They also tend to come up with seasonal promotions and menus which are worth checking out.