I got a great price for MGM from this thread,
Fat Wallet Travel. I don't know how you will fare for that particular weekend, but it's worth a shot.
FWIW, never book through a travel site. If you have any problems and need to cancel, you'll be stuck paying. Find your best price and call the hotel directly, they will match it and be much more accomodating if you need to cancel or change your reservation.