We have a friend who will be in Paris for a week in January. Three weeks ago they got a price from Hotel Jeanne d'Arc in the Marais of 99 euro per night (direct from the hotel). They just booked yesterday for 75 per night for the same room, with the last night, a Monday, at 67. I know that many Paris hotels are receiving cancellations, for both short term and long, but for you spur of the moment types out there, there could be some good pricing available now.
Incidentally, I did read in a TA review of this hotel that some rooms will be seeing renovation in the near future, and this may figure in to the pricing too, though it's still down 25% from a few weeks ago. The friend I refer to is young, and sleeps through nearly anything, and they are not concerned with some extra noise. Oh to be young again.
Oh and also: this rate is non cancel-able, non refundable, more derring do by youngsters.