A story in this morning's Sabah newspaper, of which I can give ony sketchy details since I don't really speak Turkish, reports that one of these clubs has been busted and several people have been charged with a variety of crimes carrying sentences of 50-75 years (!).

I think it says that a Japanese tourist refused to pay and was pushed to the ground, beaten and robbed.

Two other Spanish tourists complained of similar experiences at the same place - the Miami Disco in Aksaray, saying the were charged 1250YTL (~$850) for a glass of water.

I'm not sure how closely this is related to the OPs and others' experiences, since Aksaray is a bit far from Istiklal and is more the place that people would go looking for..um...working ladies.

Bt nonetheless, someone has actually decided to pursue this.

Links in turkish here and here

Maybe someone else can translate.