As Paris is a very touristy city, hotels are typically quite dear. Around the conference venue, there are three hotels which are 3 stars and below 150 euros per night:
Hôtel Libertel Austerlitz Jardin des Plantes
This is a non-exhaustive list. The venue is a 10 minute walk from Paris Austerlitz, which services the RER C, ligne 10 and ligne 5. Hence, one can find a hotel along these lines and a 3 star hotel should be sufficient.
A general advisement, hotels can charge around 20-25 euros a day for breakfast. On average, local Boulangeries (bakeries) are good and one can find a Croissant or Pain au chocolat for less than 2 euros.
