Cheap Grocery store in Prague?

Hello everyone, I'm visiting Prague this week, and I will be in a hotel. I only have breakfast included, so I have to eat outside. I don't want to eat in restaurant everyday, as it would be too expensive, so I was thinking to buy something in stores, like bread etc. I was thinking something like Lidl or Aldi, but I don't know if they are popular, or if there's some typical store in Prague Thank you in advance :)