I agree with LAS (my hometown). Depending on the dates - low cost airfare (WN hub), low cost rooms, no need to rent a car, great dining options. For a conference for 500 people shop around for a good deal. For a group of that size take a look at Tropicana, Orleans, Westgate and The Plaza (Downtown) for low cost. Most people do not think of these four properties (especially The Plaza) when booking small conventions/conferences/meetings. Think outside the box. All four I mention would love to host your event. Pit them with the bigger/nicer facilities. Make them fight for your business. Good luck!