underground bars, concerts, cheap food in the city

hey ! I am going to visit Budapest this September. I saved some places, planning to go sightseeing, also to some bars, coffee places, and maybe visit a concert. can you please recommend:

1. underground bars/pubs

2. places where to see concerts of like some jazz, punk/hardcore or alternative stuff

3. cheap supermarkets or restaurants (I'm not looking for anything fancy, just plain regular food)

will appreciate any feedback or additional info I need for my trip. looking forward to visit <3