Nanjie bar offers 60 yuan open bar every day from 5 to 9.
But they have the worst quality of fake alcohol I've ever witnessed. You'd be better off drinking 5 yuan baijiu.
So far the best mix of quality, price and environment I've come upon was at Club13 in Wudaokou. I remember they have 10 yuan tall glasses of whiskey coke, and other cocktails, and the alcohol tastes really good (especially for the price). They apparently change the deal every day, so you might not get the chance to enjoy your favorite drink for a low price, and you'd better enjoy rock music and loud metal concerts.

Enoterra has a buy-one-get-one-free deal on wine per glass from 4-8pm every day.
Blue Frog also has a two for one deal on all drinks from 4-8 every day.