Ah, a bargain challenge. This is one of my favorite things. There are many good suggestions but here's what Mr. Lion would do:
Go to one of the hotel web pages that has on-line booking such as
www.mandalaybay.com and look at the calendar of available dates. This will give you a good idea of when the lighter times are. Currently the first three weekends in December look good and everything else is wicked expensive.
Next, go to
www.unitedvacations.com and book a HOTEL-ONLY package for the weekend you've selected. This will give you a big list of bargain rates at many hotels for you to choose from.
Then I would compare these rates with
www.lvrs.com and
www.expedia.com to see if they have any improvement.
Finally, when you've narrowed it down to two or three hotels, call the hotels directly on the off chance they can get you a better rate. Most likely they cannot.
If you want any recommendations about specific places, feel free to ask! And have fun in the most exciting city in the world!