A $500 hold for 4 - 5 nights in NYC ($100/day) doesn't sound excessive. Hotels with a minibar in the room will often hold the total value of the minibar. You might be able to reduce what they hold by refusing a minibar key. If you're attending a conference where all meals are provided by the conference, you could also use that as a negotiating point. Ask at the front desk when you check in and see what they say. I'm sure you know that the hold may last for a week or more after you check out. Just be prepared to have that money tied up for some time.