I'm sure there's rooms available for Mardi Gras right now, almost anywhere you want.
They're a bit pricey, the closer you get to Bourbon St. But, if you want a room it's going to probably require a 4-5 night-minimum.

One of the best hotels to stay at is the Royal Sonesta on Bourbon St. Ask how much a Bourbon St Balcony room is. It's fun to watch all of the mayhem from above! If you want something outside the French Quarter, the rooms are going to be less expensive. Staying in the Warehouse District is a VERY cool option, because you're close to the FQ and lots of the big parades pass within a couple blocks of your hotel......Give those a try...Marriott Courtyard, Embassy Suites....Just to name a couple.

-Gene