I did this a year ago, excellent fun. Usually a 2 hour minimum applies though. Cost was around 200$ total including full bar. (2 hour trip). Thing is, its the same price whether you are 2 or 6 people. Good deal if 6 of you go, a little pricey if only 2 go, i.e. just a couple thing.

Found the company via the internet, unfortunately I cant remember the name..