Hotel restaurants may be expensive (although some of the budget hotels provide a free or low-cost breakfast buffet), but convenience store food is not your only alternative.
Japan has more hole-in-the-wall restaurants than you'll believe if you haven't been there, and just about any place you can afford is going to have either plastic models or photos of the food in the window, labeled with prices. What you see is what you get in terms of both food and price, since the listed price includes taxes and service, so no tipping.
If the server doesn't speak English, simply point to what you want.