Just a tip for when you're looking at the prices of hotels - if you're not fixed to travelling a particular week, check out prices over a few different weeks. If there are big conferences or events during a particular week, the room prices shoot up, and it can be hard to even find a room.
We went for my birthday this year, and booked flights for the 6th Feb. Little did I know, that was day of the Superbowl, and millions (it seems!) flock to Vegas to bet on the game. It was really hard to get a room, although we ended up at the Mirage, which was lovely. It was relatively expensive though - we paid something like £500 for 4 nights.
The other thing to do is sign up for email offers from the hotels on their websites - hotels like the Venetian and the Bellagio offer rooms as low as $100 midweek during quieter periods.
Have fun planning!