I think the best way is to start by checking to see if there is anything going at the time you'd be in Vegas that could negatively impact the price of the room. I would book directly with the hotel and note the cancellation policy. You can always re-book with the lower room rates if they become available. Then within one week of arrival and not within the no-cancellation window I would hit priceline. If i get what I want, then I cancel with the hotel.