No shit, I just read the reviews. Berch. On the other hand, I'm looking at the Suitehotel which is very close and, though quite more expensive, looks like a good deal. The Ibis is a bit cheapre but not as nice.
If you're going for the very, very cheap option, try the youth hostels instead. You'll get a level of quality similar to those of a 1-star or the 2-low-star hotels, but at best prices.
As for the zone of Montreuil, it's not very nice... but that's where the convention is being held. If you don't mind taking the tube to the expo, a good part to look at is the zone of Bastille and Opera: it's not too centric so the accomodations aren't very expensive, but it's an OK quarter. Beware of Montmartre! It's very touristic by day, but at night it might be dreary depending of which parts.