Because I'm reasonably close to London, the Eurostar's the most convenient way for me, as well as probably the cheapest.
I'm staying at a hotel quite close to Gare du Nord, as I have to catch an early train back home the next day in order to celebrate my girlfriend's birthday with her. However, while I was looking for a place to stay, I did consider this place, which is across the road from the concert hall and is 35 Euro a night for a single room with shared bathroom and toilet:
Hotel de Paris, La Villette