I am listing below the cheapest venues for drinking and partying in Istanbul. They are all popular with students (in particular those who joined the Erasmus program) and backpackers. On average, it will cost you 5$ for a cocktail and 3-4$ for a large beer. Most have a free entrance.
Papillon
Located on the 4th floor of a building on Balo Sokak, this intimate bar sells beer and shots for less than 2$. Come before midnight for even lower prices. Not easy to find, it is more a home than a real bar.
Ritim
Rooftop bar usually part of the city's pub crawl and Erasmus nights. Crowded. Lots of backpackers/young tourists. Good option if you are hoping to find a girl/guy for the night as they organize regular singles parties. Music is everything that makes people dance like reggaeton, hip-hop, salsa, Rumba, Gypsy music or R&B. The entrance is free, the pint of beer costs about 4$ after midnight, less before (happy hours). Open every day until 5am.
Ritim
Araf
Araf is a rooftop bar with live world music every night starting 11.30pm. Many of its clients are not exactly clubbers like the ones you will find in Ritim or Papillon. They come to sip on a drink and discuss with friends. Good atmosphere and interesting crowd.
Eski Beyrut
Possibly the most popular meeting point for Erasmus student, I'm sure you could find 30 nationalities there at least every night. Eski Beyrut is a well-run bar/club with cheap alcohol, clean facilities, smart marketing and mainstream music (top 40 hits, Rn'B). Good pick up place.
Eski Beyrut
Beat
Beat is similar to Eski Beyrut, only bigger. The crowd may not be as sophisticated though. With 2 floors including a rooftop, it has 2 types of electronic music: EDM (mainstream) and underground (trance, minimal, techno). Free entrance except on Saturdays. Drinks around 15TL for a cocktail.
If you are really broke and you want to drink for as cheap as possible, you can also head to one of the numerous Müzikhol or Turky bars of Istanbul. Those small dive bars generally serve alcohol in very simple settings with Turkish pop music in the background. You will find them everywhere. Those were in Kadiköy:
