If you are in Tokyo, there are many Yoshinoya you can find, the leading restaurant of beef bowl.
I had this lunch. There are three sizes, this is the smallest and I also ordered miso soup, which is 50 yen. The total was 430 yen.
Usually, lunch set menu is around 1000 yen ( 600 yen to 1200 yen is the range , I would say). Compared to those, it feels quite reasonable and when you don't have much time , nice enough. ( at least for myself ! )