I'm going there this week so any help about good and affordable restaurants would be helpful
Thanks in advance
Try the small burger places in Taksim square. They have delicious doner kebab and burgers. You may also want to eat "iskender" while you are in Istanbul. You can also find it in Taksim, there is a restaurant called "Bursa Iskender" Addresse: Atıf Yılmaz Cd. (Ağa Camii sokağı) No: 8 Beyoğlu / İstanbul
I also recommend you to go to Karakoy and try the baklava in "Gulluoglu Baklava". You will never forget this. You can also try the fish sandwiches in Karakoy. These are some local tips. I hope it helps.
I tried that, it's really delicious.