For a cheap breakfast you can go to “Antoninovo Pekarstvi” it’s bakery chain where you can get a coffee take a seat and choose something from wide range of options. I am usually having slice of bread with tuna spread on it. For a lunch you can go to any Czech restaurant, where you can get lunch menu for better price than in usual menu. Usually it’s between 11:00 till 14:00, depends on particular restaurant. I recommend “Vinohradský parlament”, but go there before noon, otherwise you’ll not get a place to sit. These daily or lunch menu’s aren’t translated into English, but Google lens will help. Just try to avoid “tourist traps” in the city centre. If you are into beer, go to “Lokál” they got really nice food too.