Eating out in Japan can be extremely cheap, not just ramen. You don't have to worry, as you can seek out the budget options for almost every type of food. There is expensive high-end sushi but at the same time dirt cheap sushi that is fine as well.
Bentos are not worth the cost, especially for foreigners who are used to eating more than the Japanese do.
My blog has articles on Japanese food that can give you more ideas -
Smart & Cheap Japan Travel