There are alot of good halls in Amman either in hotels or outside; as for prices .. I think you should personally contact each to check for their seasonal offers and prices as they differ from one place to another and also depends on what you exactly need the hall for. For great hotel halls and relatively good deals check @Le Meridien Amman Hotel @Landmark Amman Hotel
@Jeneva hotel @Bristol Amman Hotel @Ayass Hotel also the outdoors space next to the pool at @Grand Hyatt Amman Hotel and @Days Inn