Hey, there's a site called
Prom Night Events which our grade used last year, and they actually bundle things for you so it makes everything easy =) your venue, DJ, photographer, food, everything's there. Many choices. Also you get to choose your extras: whether or not you want certain types of decorations, slushie bars, even roses, to name a few. How much of these extras you want determines the final price, and I'm sure most (if not all) of the venues accommodate 150-200 people.
Good luck