I think there's a youth hostel there...
well, if you're deadset on staying in Monaco, I personally cannot help you, but from what I hear, Nice is about a 20 minute train ride to Monaco, and much cheaper, so its more worth your while to stay there, and then just go to Monaco for the day.
"Sir, you're drunk!"
"And you're ugly. But tomorrow I will be sober, and you will still be ugly."