"Cheap" hotel in central Paris

[AuldAlliance]

Can anyone recommend a clean, peaceful hotel in central Paris for around 90e a night? (Apparently cheap for Paris....)
Proximity and/or easy metro access to rue de la Médecine (Sorbonne Nouvelle) and avenue Charles V (Uni. Paris 7) preferred, as I have to flit between the two. I realise I can't have proximity to both, but proximity to one and good access to the other would be nice.
TIA.

I stayed here with my friend and it was fine.

Last summer we stayed in a Citadines apartment hotel and only paid 100e a night as they were having a 48 hour sale, with various of their Paris locations at half price. We had one night in an older apartment on our way south and a long weekend on the way back in the Bastille/Marais location. Both were clean, quiet, with kitchenette, sofabed and 1 bedroom. Worth keeping an eye on their website.

Sorry for not acknowledging your replies, I was lost in la France profonde and had no Internet access.

Will check both of those out.