Ohhh yes, the beer (Efes) is fantastic.
Cheapest - well it seems to be much of a muchness the prices all over. If you really want to go "cheap" though - just buy it from a supermarket, and chill it in your fridge back at the apartment, then pour yourself a cool one sat on the balcony
That's good to do at the end of an evening, but you want to be sat in a bar people watching, it's not too expensive really.