Turn up on a Sunday or Monday (except labour day) mid afternoon (so you have time to shop around) and have a brass neck. What price can you do me? Is that your best rate? What can I do to make the rate cheaper (this sounds daft but some will offer a better room rate if you have breakfast or stay for an extra night etc.
Most car hire places, leaflet hander outers and shops have booklets of vouchers for good deals starting on these days.
i found circus circus to be very reasonable (its at the end of the strip), think it was only about $40 for the room for the night, that was a few years ago tho. its was excellent value for money